disp: msm: dp: avoid using freed panel for dp mst

The inactive simulated DP MST connectors will not have a panel assigned.
So, the driver needs check for a valid panel before dereferencing the
panel object.

Change-Id: I60a4ca666f3c7c81a4e92e08cf572d5abac4ee78
Signed-off-by: Sankeerth Billakanti <quic_sbillaka@quicinc.com>

msm/dp/dp_debug.c

@@ -1777,8 +1777,10 @@ static void dp_debug_set_sim_mode(struct dp_debug_private *debug, bool sim)
 		display = sde_conn->display;
 		if (display->base_connector == (*debug->connector)) {
 			panel = sde_conn->drv_panel;
-			panel->mode_override = false;
-			panel->mst_hide = false;
+			if (panel) {
+				panel->mode_override = false;
+				panel->mst_hide = false;
+			}
 		}
 	}
 	drm_connector_list_iter_end(&conn_iter);