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: NOleksij Rempel <bug-track@fisher-privat.net>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/b43/b43.h

@@ -877,6 +877,10 @@ struct b43_wl {
 	 * from the mac80211 subsystem. */
 	u16 mac80211_initially_registered_queues;
 
+	/* Set this if we call ieee80211_register_hw() and check if we call
+	 * ieee80211_unregister_hw(). */
+	bool hw_registred;
+
 	/* We can only have one operating interface (802.11 core)
 	 * at a time. General information about this interface follows.
 	 */

drivers/net/wireless/b43/main.c

@@ -2437,6 +2437,7 @@ static void b43_request_firmware(struct work_struct *work)
 	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 @@ static struct b43_wl *b43_wireless_init(struct b43_bus_dev *dev)
 
 	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 @@ static void b43_bcma_remove(struct bcma_device *core)
 	 * as the ieee80211 unreg will destroy the workqueue. */
 	cancel_work_sync(&wldev->restart_work);
 
+	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 @@ static void b43_ssb_remove(struct ssb_device *sdev)
 	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. */