qcacmn: Detach scan object on release memory callback

Detach scan start request object from serialization object
on release memory callback. It's requred as some times
serialization ends up calling callback funtcions even after
calling release memory command due to race conditions.

Change-Id: Id0f74032de40bad679c27fe3e5ab1bf83e6dfcf5
CRs-Fixed: 2208227

umac/scan/core/src/wlan_scan_manager.c

@@ -351,6 +351,7 @@ scm_scan_serialize_callback(struct wlan_serialization_command *cmd,
 		/* command successfully completed.
 		 * Release vdev reference and free scan_start_request memory
 		 */
+		cmd->umac_cmd = NULL;
 		wlan_objmgr_vdev_release_ref(req->vdev, WLAN_SCAN_ID);
 		status = scm_scan_free_scan_request_mem(req);
 		break;