rt2x00: Use unlikely for unexpected error condition in rt2x00_mac_tx

rt2x00queue_write_tx_frame is unlikely to fail. Tell the compiler.
Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rt2x00/rt2x00mac.c

@@ -149,7 +149,7 @@ void rt2x00mac_tx(struct ieee80211_hw *hw, struct sk_buff *skb)
 			goto exit_fail;
 	}
 
-	if (rt2x00queue_write_tx_frame(queue, skb, false))
+	if (unlikely(rt2x00queue_write_tx_frame(queue, skb, false)))
 		goto exit_fail;
 
 	if (rt2x00queue_threshold(queue))