update msc driver to pass MSC BOT error recovery compliant test

examples/device/msc_dual_lun/src/msc_disk_dual.c

@@ -274,6 +274,17 @@ int32_t tud_msc_read10_cb(uint8_t lun, uint32_t lba, uint32_t offset, void* buff
   return bufsize;
 }
 
+bool tud_msc_is_writable_cb (uint8_t lun)
+{
+  (void) lun;
+
+#ifdef CFG_EXAMPLE_MSC_READONLY
+  return false;
+#else
+  return true;
+#endif
+}
+
 // Callback invoked when received WRITE10 command.
 // Process data in buffer to disk's storage and return number of written bytes
 int32_t tud_msc_write10_cb(uint8_t lun, uint32_t lba, uint32_t offset, uint8_t* buffer, uint32_t bufsize)