qcacld-3.0: Fix ACS failure if no AP is found during scan

If no AP is found in scan req for ACS, the get scan results return
error E_EMPTY. But th ACS need error E_NULL_VALUE to find a valid
channel if scan results are empty.

To fix this Return E_NULL_VALUE instead of E_EMPTY, if scan results
are empty.

Change-Id: Id50eb66e89881d4a763084037bd5576eb500bb68
CRs-Fixed: 2057618

core/sme/src/csr/csr_api_scan.c

@@ -5709,7 +5709,7 @@ QDF_STATUS csr_scan_get_result(tpAniSirGlobal mac_ctx,
 
 	if (!list || !qdf_list_size(list)) {
 		sme_err("get scan result failed");
-		status = QDF_STATUS_E_EMPTY;
+		status = QDF_STATUS_E_NULL_VALUE;
 		goto error;
 	}