An Oops has once been observed, when the SDIO card had been ejected during
IO. The PC value shows, that the dev pointer in b43_op_stop() was NULL.
(I moved the NULL check before the lock, based upon a suggestion from
Julian Calaby <julian.calaby@gmail.com>. -- JWL)
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>