drm/amd/display: Return error code on DSC atomic check failure

[Why&How]
We were not returning -EINVAL on DSC atomic check fail. Add it.

Fixes: 71be4b16 ("drm/amd/display: dsc validate fail not pass to atomic check")
Reviewed-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Hersen Wu <hersenxs.wu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -10170,6 +10170,7 @@ static int amdgpu_dm_atomic_check(struct drm_device *dev,
 		ret = compute_mst_dsc_configs_for_state(state, dm_state->context, vars);
 		if (ret) {
 			DRM_DEBUG_DRIVER("compute_mst_dsc_configs_for_state() failed\n");
+			ret = -EINVAL;
 			goto fail;
 		}
 

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

@@ -1410,6 +1410,7 @@ int pre_validate_dsc(struct drm_atomic_state *state,
 	ret = pre_compute_mst_dsc_configs_for_state(state, local_dc_state, vars);
 	if (ret != 0) {
 		DRM_INFO_ONCE("pre_compute_mst_dsc_configs_for_state() failed\n");
+		ret = -EINVAL;
 		goto clean_exit;
 	}