b43: Avoid possible double calls to b43_one_core_detach()

In b43_request_firmware(), when ieee80211_register_hw() fails,
b43_one_core_detach() is called. In b43_bcma_remove() and
b43_ssb_remove(), b43_one_core_detach() is called again. In this case,
null-pointer dereferences and double-free problems can occur when
the driver is removed.

To fix this bug, the call to b43_one_core_detach() in
b43_request_firmware() is deleted.

This bug is found by a runtime fuzzing tool named FIZZER written by us.

Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>