iwlwifi: error checking for number of tfds in queue

When receive reply_tx and ready to decrement the count for number of
tfds in queue, do error checking to prevent error condition and
tfds_in_queue become negative number.

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
CC: stable@kernel.org
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/iwlwifi/iwl-5000.c b/drivers/net/wireless/iwlwifi/iwl-5000.c
index de45f30..f27c514 100644
--- a/drivers/net/wireless/iwlwifi/iwl-5000.c
+++ b/drivers/net/wireless/iwlwifi/iwl-5000.c
@@ -1125,7 +1125,7 @@
 					scd_ssn , index, txq_id, txq->swq_id);
 
 			freed = iwl_tx_queue_reclaim(priv, txq_id, index);
-			priv->stations[sta_id].tid[tid].tfds_in_queue -= freed;
+			iwl_free_tfds_in_queue(priv, sta_id, tid, freed);
 
 			if (priv->mac80211_registered &&
 			    (iwl_queue_space(&txq->q) > txq->q.low_mark) &&
@@ -1154,7 +1154,7 @@
 
 		freed = iwl_tx_queue_reclaim(priv, txq_id, index);
 		if (ieee80211_is_data_qos(tx_resp->frame_ctrl))
-			priv->stations[sta_id].tid[tid].tfds_in_queue -= freed;
+			iwl_free_tfds_in_queue(priv, sta_id, tid, freed);
 
 		if (priv->mac80211_registered &&
 		    (iwl_queue_space(&txq->q) > txq->q.low_mark))