staging: greybus: mark expected switch fall-through in check_urb_status

In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where we are expecting to fall through.
Signed-off-by: NGustavo A. R. Silva <garsilva@embeddedor.com>
Acked-by: NJohan Hovold <johan@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/greybus/es2.c

@@ -761,6 +761,7 @@ static int check_urb_status(struct urb *urb)
 	case -EOVERFLOW:
 		dev_err(dev, "%s: overflow actual length is %d\n",
 			__func__, urb->actual_length);
+		/* fall through */
 	case -ECONNRESET:
 	case -ENOENT:
 	case -ESHUTDOWN: