b43: Fix Bugzilla #14181 and the bug from the previous 'fix'

"b43: Fix PPC crash in rfkill polling on unload" fixed the bug reported
in Bugzilla No. 14181; however, it introduced a new bug. Whenever the
radio switch was turned off, it was necessary to unload and reload
the driver for it to recognize the switch again.

This patch fixes both the original bug in #14181 and the bug introduced by
the previous patch. It must be stated, however, that if there is a BCM4306/3
with an rfkill switch (not yet proven), then the driver will need an
unload/reload cycle to turn the device back on.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>