wl12xx: check if elp wakeup failed

Check the return call from wl12xx_ps_elp_wakeup() and bail out if it
fails. This shouldn't happen, but if does there's a fundamental low
level issue.

Signed-off-by: Kalle Valo <kalle.valo@nokia.com>
Reviewed-by: Luciano Coelho <luciano.coelho@nokia.com>
Reviewed-by: Vidhya Govindan <vidhya.govindan@nokia.com>
Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/wl12xx/wl1251_tx.c

@@ -311,7 +311,9 @@ void wl1251_tx_work(struct work_struct *work)
 
 	while ((skb = skb_dequeue(&wl->tx_queue))) {
 		if (!woken_up) {
-			wl12xx_ps_elp_wakeup(wl);
+			ret = wl12xx_ps_elp_wakeup(wl);
+			if (ret < 0)
+				goto out;
 			woken_up = true;
 		}