wl1251: fix NULL pointer dereference

wl1251: fix NULL pointer dereference
Signed-off-by: NPali Rohár <pali.rohar@gmail.com>
Reported-by: NFelipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: NPavel Machek <pavel@ucw.cz>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ti/wl1251/event.c

@@ -124,7 +124,7 @@ static int wl1251_event_process(struct wl1251 *wl, struct event_mailbox *mbox)
 			return ret;
 	}
 
-	if (vector & SYNCHRONIZATION_TIMEOUT_EVENT_ID) {
+	if (wl->vif && vector & SYNCHRONIZATION_TIMEOUT_EVENT_ID) {
 		wl1251_debug(DEBUG_EVENT, "SYNCHRONIZATION_TIMEOUT_EVENT");
 
 		/* indicate to the stack, that beacons have been lost */