fix variable names. add itf n callbacks to multihid

examples/device/hid_multipleinterface/src/usb_descriptors.c

@@ -83,13 +83,13 @@ uint8_t desc_hid_report2[] =
 // Invoked when received GET HID REPORT DESCRIPTOR
 // Application return pointer to descriptor
 // Descriptor contents must exist long enough for transfer to complete
-uint8_t const * tud_hid_descriptor_report_cb(uint8_t desc_index)
+uint8_t const * tud_hid_n_descriptor_report_cb(uint8_t itf)
 {
-  if (desc_index == 0)
+  if (itf == 0)
 	{
 		return desc_hid_report1;
 	}
-	else if (desc_index == 1)
+	else if (itf == 1)
 	{
 		return desc_hid_report2;
 	}