rt2x00: do not flush empty queue

Signed-off-by: NStanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: NKalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/ralink/rt2x00/rt2x00mac.c

@@ -743,7 +743,8 @@ void rt2x00mac_flush(struct ieee80211_hw *hw, struct ieee80211_vif *vif,
 		return;
 
 	tx_queue_for_each(rt2x00dev, queue)
-		rt2x00queue_flush_queue(queue, drop);
+		if (!rt2x00queue_empty(queue))
+			rt2x00queue_flush_queue(queue, drop);
 }
 EXPORT_SYMBOL_GPL(rt2x00mac_flush);