b43: Don't abuse wl->current_dev in the led work

Don't abuse wl->current_dev in the LED work for checking whether we're
going down. Add an explicit variable.
This fixes a crash on rmmod dereferencing the wl->current_dev NULL pointer
in various other places of the driver.

Signed-off-by: Michael Buesch <mb@bu3sch.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/b43/leds.c b/drivers/net/wireless/b43/leds.c
index ac5a322..fbe31e0 100644
--- a/drivers/net/wireless/b43/leds.c
+++ b/drivers/net/wireless/b43/leds.c
@@ -112,10 +112,7 @@
 	struct b43_led *led = container_of(led_dev, struct b43_led, led_dev);
 	struct b43_wl *wl = led->wl;
 
-	/* The check for current_dev is only needed while unregistering,
-	 * so it is sequencial and does not race. But we must not dereference
-	 * current_dev here. */
-	if (likely(wl->current_dev)) {
+	if (likely(!wl->leds.stop)) {
 		atomic_set(&led->state, brightness);
 		ieee80211_queue_work(wl->hw, &wl->leds.work);
 	}
@@ -314,6 +311,8 @@
 			break;
 		}
 	}
+
+	dev->wl->leds.stop = 0;
 }
 
 void b43_leds_exit(struct b43_wldev *dev)