qcacld-3.0: Possible mem leak in sme_set_miracast

In sme_set_miracast If mac_ptr is NULL and qdf_mem_malloc(sizeof(*val))
returns success, driver returns without qdf_mem_free for val.
This results in memory leak in sme_set_miracast.

Allocate mem for val only if mac_ptr is valid.

Change-Id: I98a6f0acc9452f7f04aa4949fc8efe21b260fac7
CRs-Fixed: 2465861