wl1251: fix crash on remove due to leftover work item

This driver currently leaves elp_work behind when stopping, which
occasionally results in data corruption because work function ends
up accessing freed memory, typical symptoms of this are various
worker_thread crashes. Fix it by cancelling elp_work.

Cc: stable@vger.kernel.org # v2.6.37+
Signed-off-by: Grazvydas Ignotas <notasas@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/wl1251/main.c

@@ -479,6 +479,7 @@ static void wl1251_op_stop(struct ieee80211_hw *hw)
 	cancel_work_sync(&wl->irq_work);
 	cancel_work_sync(&wl->tx_work);
 	cancel_work_sync(&wl->filter_work);
+	cancel_delayed_work_sync(&wl->elp_work);
 
 	mutex_lock(&wl->mutex);