b43: Fix PPC crash in rfkill polling on unload

In Bugzilla No. 14181, a PowerMac G4 crashes on ifdown or
module unload because the rfkill polling has not been stopped.
For the x86 architectures, the attempt to reach a now unmapped
register is not fatal as it is on PPC.

(Includes "b43: Fix locking problem when stopping rfkill polling". -- JWL)
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/b43/main.c

@@ -4501,6 +4501,7 @@ static void b43_op_stop(struct ieee80211_hw *hw)
 
 	cancel_work_sync(&(wl->beacon_update_trigger));
 
+	wiphy_rfkill_stop_polling(hw->wiphy);
 	mutex_lock(&wl->mutex);
 	if (b43_status(dev) >= B43_STAT_STARTED) {
 		dev = b43_wireless_core_stop(dev);