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

In the Linux kernel, the following vulnerability has been resolved:

wifi: 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.