qcacld-3.0: Validate mac context in csr_get_peer_rssi_cb

Currently mac context is validated in csr_get_peer_rssi_cb
but even in case of invalid mac context it is dereferenced.

Add a check to validate the mac context and gracefully
return in case of invalid address

Change-Id: I96181e7ecd7be1a18e644f9499137a42e6af6372
CRs-Fixed: 2673557

core/sme/src/csr/csr_api_roam.c

@@ -6338,12 +6338,16 @@ static void csr_get_peer_rssi_cb(struct stats_event *ev, void *cookie)
 {
 	struct mac_context *mac = (struct mac_context *)cookie;
 
-	if (!mac)
-		goto disconnect_stats_complete;
+	if (!mac) {
+		sme_err("Invalid mac ctx");
+		return;
+	}
+
 	if (!ev->peer_stats) {
 		sme_debug("%s no peer stats\n", __func__);
 		goto disconnect_stats_complete;
 	}
+
 	mac->peer_rssi = ev->peer_stats->peer_rssi;
 	mac->peer_txrate = ev->peer_stats->tx_rate;
 	mac->peer_rxrate = ev->peer_stats->rx_rate;