drm/amd/display: MST atomic_get_property missing.

Missing function implementation was leading to EINVAL
in UMD thus not adding MST connector to X topology
and hence not getting set mode for it.
Signed-off-by: Andrey Grodzovsky <Andrey.Grodzovsky@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -168,7 +168,8 @@ static const struct drm_connector_funcs dm_dp_mst_connector_funcs = {
 	.reset = amdgpu_dm_connector_funcs_reset,
 	.atomic_duplicate_state = amdgpu_dm_connector_atomic_duplicate_state,
 	.atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
-	.atomic_set_property = amdgpu_dm_connector_atomic_set_property
+	.atomic_set_property = amdgpu_dm_connector_atomic_set_property,
+	.atomic_get_property = amdgpu_dm_connector_atomic_get_property
 };
 
 static int dm_dp_mst_get_modes(struct drm_connector *connector)