wlcore: take the mutex before resetting Tx queues

Otherwise we risk contention for private members of our global structure
while op_stop_locked is running.
Reported-by: NIdo Yariv <ido@wizery.com>
Signed-off-by: NArik Nemtsov <arik@wizery.com>
Signed-off-by: NLuciano Coelho <coelho@ti.com>

drivers/net/wireless/ti/wlcore/main.c

@@ -1852,8 +1852,8 @@ static void wlcore_op_stop_locked(struct wl1271 *wl)
 	cancel_delayed_work_sync(&wl->tx_watchdog_work);
 
 	/* let's notify MAC80211 about the remaining pending TX frames */
-	wl12xx_tx_reset(wl);
 	mutex_lock(&wl->mutex);
+	wl12xx_tx_reset(wl);
 
 	wl1271_power_off(wl);
 	/*