b43: do not call ieee80211_unregister_hw if we are not registred

this patch fixes kernel Oops on "rmmod b43" if firmware was not loaded:

BUG: unable to handle kernel NULL pointer dereference at 0000000000000088
IP: [<ffffffff8104e988>] drain_workqueue+0x25/0x142
PGD 153ac6067 PUD 153b82067 PMD 0
Oops: 0000 [#1] SMP

Signed-off-by: Oleksij Rempel <bug-track@fisher-privat.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/b43/main.c b/drivers/net/wireless/b43/main.c
index 5a39b22..acd03a4 100644
--- a/drivers/net/wireless/b43/main.c
+++ b/drivers/net/wireless/b43/main.c
@@ -2437,6 +2437,7 @@
 	err = ieee80211_register_hw(wl->hw);
 	if (err)
 		goto err_one_core_detach;
+	wl->hw_registred = true;
 	b43_leds_register(wl->current_dev);
 	goto out;
 
@@ -5299,6 +5300,7 @@
 
 	hw->queues = modparam_qos ? B43_QOS_QUEUE_NUM : 1;
 	wl->mac80211_initially_registered_queues = hw->queues;
+	wl->hw_registred = false;
 	hw->max_rates = 2;
 	SET_IEEE80211_DEV(hw, dev->dev);
 	if (is_valid_ether_addr(sprom->et1mac))
@@ -5370,12 +5372,15 @@
 	 * as the ieee80211 unreg will destroy the workqueue. */
 	cancel_work_sync(&wldev->restart_work);
 
-	/* Restore the queues count before unregistering, because firmware detect
-	 * might have modified it. Restoring is important, so the networking
-	 * stack can properly free resources. */
-	wl->hw->queues = wl->mac80211_initially_registered_queues;
-	b43_leds_stop(wldev);
-	ieee80211_unregister_hw(wl->hw);
+	B43_WARN_ON(!wl);
+	if (wl->current_dev == wldev && wl->hw_registred) {
+		/* Restore the queues count before unregistering, because firmware detect
+		 * might have modified it. Restoring is important, so the networking
+		 * stack can properly free resources. */
+		wl->hw->queues = wl->mac80211_initially_registered_queues;
+		b43_leds_stop(wldev);
+		ieee80211_unregister_hw(wl->hw);
+	}
 
 	b43_one_core_detach(wldev->dev);
 
@@ -5446,7 +5451,7 @@
 	cancel_work_sync(&wldev->restart_work);
 
 	B43_WARN_ON(!wl);
-	if (wl->current_dev == wldev) {
+	if (wl->current_dev == wldev && wl->hw_registred) {
 		/* Restore the queues count before unregistering, because firmware detect
 		 * might have modified it. Restoring is important, so the networking
 		 * stack can properly free resources. */