qcacmn: Fix OOB read issue in SSID ie

During beacon or probe response, if channel is dfs && frame type
is MGMT_SUBTYPE_BEACON, it would call "util_scan_add_hidden_ssid"
to deal with the packet. If the ie id matches with SSID then OOB
read may occur in ie_len as it is validated with upper bound of
ie_ssid.

Validate the ie length first. If it is more than 0 then copy
memory to SSID which are equivalent to ie length.

Change-Id: Ib5e2ab7f6f3337d4c3e5c240e3133d8f276be50a
CRs-Fixed: 3007473