wlan: First initialize and then use of pbFrames

Temporary pbFrames pointer use to read IEEE80211
mgmt frame, but type and subtype read before assigning
mgmt frame to pbFrames which leads to access a NULL pointer
to reading type and subtype of wifi frame.
The Fix is to first assign the pointer pbFrames before us of it.

Change-Id: I19209cf5d000440becd050c00cc83d1497eb89d6
CRs-Fixed: 2952681