qcacmn: Possible OOB read in process_fw_diag_event_data

API "fw_diag_data_event_handler" is the handler of an event
WMI_DIAG_DATA_CONTAINER_EVENTID comes from FW. Arguments of
this handler function come from FW.

If num_data may be less than size of(struct wlan_diag_data),
possible OOB while extracting event data.

Fix is to add a sanity check for num_data to avoid the OOB
read.

Change-Id: Ia2eb62dbaa154936bdb4ea34065657d441f12810
CRs-Fixed: 3001178