b43: Fix oops on unload when firmware not found

commit f89ff6441df06abc2d95f3ef67525923032d6283 upstream.

When b43 fails to find firmware when loaded, a subsequent unload will
oops due to calling ieee80211_unregister_hw() when the corresponding
register call was never made.

Commit 2d838bb608e2d1f6cb4280e76748cb812dc822e7 fixed the same problem
for b43legacy.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Tested-by: Markus Kanet <dvmailing@gmx.eu>
Cc: Markus Kanet <dvmailing@gmx.eu>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>