brcmfmac: cfg80211: Pass the PMK in binary instead of hex

brcmfmac: cfg80211: Pass the PMK in binary instead of hex

Apparently the hex passphrase mechanism does not work on newer
chips/firmware (e.g. BCM4387). It seems there was a simple way of
passing it in binary all along, so use that and avoid the hexification.

OpenBSD has been doing it like this from the beginning, so this should
work on all chips.

Also clear the structure before setting the PMK. This was leaking
uninitialized stack contents to the device.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Hector Martin <marcan@marcan.st>