drm/radeon: fix fence related segfault in CS

Don't return success if scheduling the IB fails, otherwise
we end up with an oops in ttm_eu_fence_buffer_objects.

Signed-off-by: Christian König <deathsimple@vodafone.de>
Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org

drivers/gpu/drm/radeon/radeon_cs.c

@@ -358,7 +358,7 @@ static int radeon_cs_ib_chunk(struct radeon_device *rdev,
 	if (r) {
 		DRM_ERROR("Failed to schedule IB !\n");
 	}
-	return 0;
+	return r;
 }
 
 static int radeon_bo_vm_update_pte(struct radeon_cs_parser *parser,