Remove unreachable code

IAR generates warning Pe111 'statement is unreachable'. In a couple of
cases, replace return statements with TU_ATTR_FALLTHROUGH; because some
compilers apparently can't figure out that the return statements are
unreachable but do whinge about an imagined fall-through without them!

examples/device/audio_4_channel_mic/src/main.c

@@ -99,9 +99,6 @@ int main(void)
     led_blinking_task();
     audio_task();
   }
-
-
-  return 0;
 }
 
 //--------------------------------------------------------------------+

examples/device/audio_test/src/main.c

@@ -100,9 +100,6 @@ int main(void)
     led_blinking_task();
     audio_task();
   }
-
-
-  return 0;
 }
 
 //--------------------------------------------------------------------+

examples/device/board_test/src/main.c

@@ -67,8 +67,6 @@ int main(void)
       led_state = 1 - led_state; // toggle
     }
   }
-
-  return 0;
 }
 
 #if CFG_TUSB_MCU == OPT_MCU_ESP32S2 || CFG_TUSB_MCU == OPT_MCU_ESP32S3

examples/device/cdc_dual_ports/src/main.c

@@ -47,8 +47,6 @@ int main(void)
     tud_task(); // tinyusb device task
     cdc_task();
   }
-
-  return 0;
 }
 
 // echo to either Serial0 or Serial1

examples/device/cdc_msc/src/main.c

@@ -65,8 +65,6 @@ int main(void)
 
     cdc_task();
   }
-
-  return 0;
 }
 
 //--------------------------------------------------------------------+

examples/device/dfu/src/main.c

@@ -82,8 +82,6 @@ int main(void)
     tud_task(); // tinyusb device task
     led_blinking_task();
   }
-
-  return 0;
 }
 
 //--------------------------------------------------------------------+

examples/device/dfu_runtime/src/main.c

@@ -77,8 +77,6 @@ int main(void)
     tud_task(); // tinyusb device task
     led_blinking_task();
   }
-
-  return 0;
 }
 
 //--------------------------------------------------------------------+

examples/device/dynamic_configuration/src/main.c

@@ -66,8 +66,6 @@ int main(void)
     cdc_task();
     midi_task();
   }
-
-  return 0;
 }
 
 //--------------------------------------------------------------------+

examples/device/hid_composite/src/main.c

@@ -67,8 +67,6 @@ int main(void)
 
     hid_task();
   }
-
-  return 0;
 }
 
 //--------------------------------------------------------------------+

examples/device/hid_generic_inout/src/main.c

@@ -88,8 +88,6 @@ int main(void)
     tud_task(); // tinyusb device task
     led_blinking_task();
   }
-
-  return 0;
 }
 
 //--------------------------------------------------------------------+

examples/device/hid_multiple_interface/src/main.c

@@ -71,8 +71,6 @@ int main(void)
 
     hid_task();
   }
-
-  return 0;
 }
 
 //--------------------------------------------------------------------+

examples/device/midi_test/src/main.c

@@ -71,9 +71,6 @@ int main(void)
     led_blinking_task();
     midi_task();
   }
-
-
-  return 0;
 }
 
 //--------------------------------------------------------------------+

examples/device/msc_dual_lun/src/main.c

@@ -62,8 +62,6 @@ int main(void)
     tud_task(); // tinyusb device task
     led_blinking_task();
   }
-
-  return 0;
 }
 
 //--------------------------------------------------------------------+

examples/device/uac2_headset/src/main.c

@@ -113,8 +113,6 @@ int main(void)
     audio_task();
     led_blinking_task();
   }
-
-  return 0;
 }
 
 //--------------------------------------------------------------------+

examples/device/usbtmc/src/main.c

@@ -63,8 +63,6 @@ int main(void)
     led_blinking_task();
     usbtmc_app_task_iter();
   }
-
-  return 0;
 }
 
 //--------------------------------------------------------------------+

examples/device/usbtmc/src/usbtmc_app.c

@@ -254,7 +254,6 @@ void usbtmc_app_task_iter(void) {
     break;
   default:
     TU_ASSERT(false,);
-    return;
   }
 }
 

examples/device/video_capture/src/main.c

@@ -66,8 +66,6 @@ int main(void)
 
     video_task();
   }
-
-  return 0;
 }
 
 //--------------------------------------------------------------------+

examples/device/webusb_serial/src/main.c

@@ -103,8 +103,6 @@ int main(void)
     webserial_task();
     led_blinking_task();
   }
-
-  return 0;
 }
 
 // send characters to both CDC and WebUSB

examples/host/cdc_msc_hid/src/main.c

@@ -62,8 +62,6 @@ int main(void)
     hid_app_task();
 #endif
   }
-
-  return 0;
 }
 
 //--------------------------------------------------------------------+

examples/host/hid_controller/src/main.c

@@ -68,8 +68,6 @@ int main(void)
     hid_app_task();
 #endif
   }
-
-  return 0;
 }
 
 //--------------------------------------------------------------------+