drm/amd/display: Fix MST topology debugfs

[why]
The drm dump_topology function was previously called on all
DP connectors. This resulted in empty topology dumps for those
connectors which weren't root MST nodes.

[how]
Make sure we only dump topology from the root MST node.
Signed-off-by: Eryk Brol <eryk.brol@amd.com>
Reviewed-by: Aurabindo Jayamohanan Pillai <Aurabindo.Pillai@amd.com>
Acked-by: Anson Jacob <Anson.Jacob@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_debugfs.c

@@ -2901,6 +2901,10 @@ static int mst_topo_show(struct seq_file *m, void *unused)
 
 		aconnector = to_amdgpu_dm_connector(connector);
 
+		/* Ensure we're only dumping the topology of a root mst node */
+		if (!aconnector->mst_mgr.mst_state)
+			continue;
+
 		seq_printf(m, "\nMST topology for connector %d\n", aconnector->connector_id);
 		drm_dp_mst_dump_topology(m, &aconnector->mst_mgr);
 	}