qcacld-3.0: Fix null pointer dereference in sme_handle_bcn_recv_start

In sme_handle_bcn_recv_start, 'mac_ctx->roam.roamSession' is not
validated for null before being passed to CSR_IS_SESSION_VALID where
dereference can occur.

Validate mac_ctx->roam.roamSession against null before passing it to
CSR_IS_SESSION_VALID.

Change-Id: I48638a320f29a906a6e8a35c000191265313b734
CRs-Fixed: 2462682
1 file changed