iwlwifi: don't update TFD free counter for invalid station

This patch makes sure that station table is not accessed
with invalid station id in 4965 TX response path

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Reported-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/iwlwifi/iwl-4965.c

@@ -2236,15 +2236,15 @@ static void iwl4965_rx_reply_tx(struct iwl_priv *priv,
 				   tx_resp->failure_frame);
 
 		freed = iwl_tx_queue_reclaim(priv, txq_id, index);
-		if (qc)
+		if (qc && likely(sta_id != IWL_INVALID_STATION))
 			priv->stations[sta_id].tid[tid].tfds_in_queue -= freed;
 
 		if (priv->mac80211_registered &&
 		    (iwl_queue_space(&txq->q) > txq->q.low_mark))
 			ieee80211_wake_queue(priv->hw, txq_id);
 	}
 
-	if (qc)
+	if (qc && likely(sta_id != IWL_INVALID_STATION))
 		iwl_txq_check_empty(priv, sta_id, tid, txq_id);
 
 	if (iwl_check_bits(status, TX_ABORT_REQUIRED_MSK))