qcacld-2.0: Fix array OOB for duplicate rate

Some IoT AP may have duplicate rates in supported rates and
extended rates in beacon, need filter them when populate peer 11a/11b
rates during connect/roaming, or array out of bound issue will happen.

Change-Id: I685e8c07ee147296bfa22742dad4210e7fa02c4a
CRs-Fixed: 3049634