usb: gadget: f_tcm: mark expected switch fall-through

In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where we are expecting to fall through.

Addresses-Coverity-ID: 703128
Signed-off-by: NGustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: NFelipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/gadget/function/f_tcm.c

@@ -1145,6 +1145,7 @@ static int usbg_submit_command(struct f_uas *fu,
 	default:
 		pr_debug_once("Unsupported prio_attr: %02x.\n",
 				cmd_iu->prio_attr);
+		/* fall through */
 	case UAS_SIMPLE_TAG:
 		cmd->prio_attr = TCM_SIMPLE_TAG;
 		break;