qcacld-3.0: Avoid OOB read in dot11f_unpack_assoc_response

Avoid OOB read in dot11f_unpack_assoc_response API. Add check
for when nBuf == len to read another byte of pBufRemaining.

Change-Id: Iccdb0b268d16f4169b8b701ade6085d47897f785
CRs-Fixed: 3042293