disp: msm: dp: null check before accessing mst panel

This change checks if the mst panel is still valid before
accessing them when MST specific debugfs nodes are used.

Change-Id: I45f63009c1bff6a83e7af60a85f953674fef6797
Signed-off-by: Rajkumar Subbiah <quic_rsubbia@quicinc.com>

msm/dp/dp_debug.c

@@ -398,6 +398,8 @@ static ssize_t dp_debug_read_crc(struct file *file, char __user *user_buff, size
 
 		sde_conn = to_sde_connector(drm_conn);
 		panel = sde_conn->drv_panel;
+		if (!panel)
+			goto bail;
 	} else {
 		panel = debug->panel;
 	}
@@ -655,6 +657,8 @@ static ssize_t dp_debug_write_mst_con_id(struct file *file,
 
 	mst_port = sde_conn->mst_port;
 	dp_panel = sde_conn->drv_panel;
+	if (!dp_panel)
+		goto out;
 
 	if (debug->dp_debug.sim_mode) {
 		dp_sim_update_port_status(debug->sim_bridge,