qcacld-3.0: Fix possible OOB read in wlan_hdd_set_sap_hwmode

A possible out-of-bound read can happen in the hdd function
wlan_hdd_set_sap_hwmode. To fix it, pass the proper length.

Change-Id: I11258c6d9f481a21afc3229762900153d6f83c82
CRs-Fixed: 2853407