qcacmn: Add null check for RNR node in scan API

Add null check for RNR node in the scan API
scm_filter_rnr_flag_pno before accessing its parameters.

CRs-Fixed: 3645688
Change-Id: I8c18c75214128496d159425c923db1be1525e298

umac/scan/core/src/wlan_scan_cache_db.c

@@ -243,6 +243,8 @@ void scm_filter_rnr_flag_pno(struct wlan_objmgr_vdev *vdev,
 			continue;
 
 		qdf_list_for_each(&chan->rnr_list, rnr_node, node) {
+			if (!rnr_node)
+				continue;
 			if (rnr_node->entry.short_ssid) {
 				if (rnr_node->entry.short_ssid == short_ssid) {
 			/* If short ssid entry present in RNR db cache, remove