b43: remove Comparison of 0/1 to bool variable in pio.c

Fix the following coccicheck warning:

drivers/net/wireless/broadcom/b43/pio.c:768:10-25: WARNING: Comparison
of 0/1 to bool variable

Signed-off-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200504113311.41026-1-yanaijie@huawei.com