rt2x00: Fix fall-through warnings for Clang

In preparation to enable -Wimplicit-fallthrough for Clang, fix a warning
by explicitly adding a break statement instead of letting the code fall
through to the next case.

Link: https://github.com/KSPP/linux/issues/115Signed-off-by: NGustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: NKalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/b0d4c50b803bc38ed370521b9b0a44365cae9386.1605896060.git.gustavoars@kernel.org

drivers/net/wireless/ralink/rt2x00/rt2x00queue.c

@@ -941,6 +941,7 @@ void rt2x00queue_unpause_queue(struct data_queue *queue)
 		 * receive frames.
 		 */
 		queue->rt2x00dev->ops->lib->kick_queue(queue);
+		break;
 	default:
 		break;
 	}