ALSA: caiaq: Add fall-through annotation

As a preparatory patch for the upcoming -Wimplicit-fallthrough
compiler checks, add the "fall through" annotation in caiaq driver.
Note that this seems necessary to be put exactly before the next
label, so it's outside the ifdef block.
Signed-off-by: NTakashi Iwai <tiwai@suse.de>

sound/usb/caiaq/device.c

@@ -200,6 +200,7 @@ static void usb_ep1_command_reply_dispatch (struct urb* urb)
 			break;
 		}
 #ifdef CONFIG_SND_USB_CAIAQ_INPUT
+		/* fall through */
 	case EP1_CMD_READ_ERP:
 	case EP1_CMD_READ_ANALOG:
 		snd_usb_caiaq_input_dispatch(cdev, buf, urb->actual_length);