qcacld-3.0: Reset global saved command to avoid double free
Reset the global saved scan command to avoid double free.
In sme_process_set_hw_mode_resp(), after freeing the local
saved_cmd pointer, the global mac->sme.saved_scan_cmd is
not reset to NULL. This ends up in double free in
csr_scan_complete()->csr_handle_nxt_cmd() where we are
still holding a stale pointer.
CRs-Fixed: 941130
Change-Id: Ibb93b8d8e601936c7996518f21646e2c140cbd20