b43: Fix rfkill allocation leakage in error paths

We must kill rfkill in any error paths that trigger after rfkill init.

Signed-off-by: Michael Buesch <mb@bu3sch.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>