ath9k_htc: Protect ampdu_action with a mutex

This is required when issuing commands to the firmware.
Signed-off-by: NSujith Manoharan <Sujith.Manoharan@atheros.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/htc_drv_main.c

@@ -1639,6 +1639,8 @@ static int ath9k_htc_ampdu_action(struct ieee80211_hw *hw,
 	struct ath9k_htc_sta *ista;
 	int ret = 0;
 
+	mutex_lock(&priv->mutex);
+
 	switch (action) {
 	case IEEE80211_AMPDU_RX_START:
 		break;
@@ -1663,6 +1665,8 @@ static int ath9k_htc_ampdu_action(struct ieee80211_hw *hw,
 		ath_err(ath9k_hw_common(priv->ah), "Unknown AMPDU action\n");
 	}
 
+	mutex_unlock(&priv->mutex);
+
 	return ret;
 }