drm/dp_mst: Don't cache EDIDs for physical ports

Caching EDIDs for physical ports prevents updating the EDID if a port
gets reconnected via a Connection Status Notification message, fix this.

Fixes: db1a0795 ("drm/dp_mst: Handle SST-only branch device case")
Cc: Wayne Lin <Wayne.Lin@amd.com>
Cc: Lyude Paul <lyude@redhat.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210201120145.350258-2-imre.deak@intel.com
(cherry picked from commit 46809153)
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>

drivers/gpu/drm/drm_dp_mst_topology.c

@@ -2302,7 +2302,8 @@ drm_dp_mst_port_add_connector(struct drm_dp_mst_branch *mstb,
 	}
 
 	if (port->pdt != DP_PEER_DEVICE_NONE &&
-	    drm_dp_mst_is_end_device(port->pdt, port->mcs)) {
+	    drm_dp_mst_is_end_device(port->pdt, port->mcs) &&
+	    port->port_num >= DP_MST_LOGICAL_PORT_0) {
 		port->cached_edid = drm_get_edid(port->connector,
 						 &port->aux.ddc);
 		drm_connector_set_tile_property(port->connector);