drm/amd/display: Catch errors from drm_atomic_helper_suspend()

drm_atomic_helper_suspend() can return PTR_ERR(), in which case the
error gets stored into `dm->cached_state`.  This can cause failures
during resume.  Catch the error during suspend and fail the suspend
instead.

Link: https://gitlab.freedesktop.org/drm/amd/-/issues/2362Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -2698,6 +2698,8 @@ static int dm_suspend(void *handle)
 
 	WARN_ON(adev->dm.cached_state);
 	adev->dm.cached_state = drm_atomic_helper_suspend(adev_to_drm(adev));
+	if (IS_ERR(adev->dm.cached_state))
+		return PTR_ERR(adev->dm.cached_state);
 
 	s3_handle_mst(adev_to_drm(adev), true);