brcmfmac: use true,false for bool variable

Fixes coccicheck warning:

drivers/net/wireless/broadcom/brcm80211/brcmfmac/fwsignal.c:911:2-24: WARNING: Assignment of 0/1 to bool variable

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>