drm/ttm: minor cleanup to move to system

resource free already sets the domain to system, and old_mem
isn't really needed.
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201020010319.1692445-3-airlied@gmail.com

drivers/gpu/drm/ttm/ttm_bo_util.c

@@ -68,10 +68,9 @@ int ttm_bo_move_to_new_tt_mem(struct ttm_buffer_object *bo,
 int ttm_bo_move_to_system(struct ttm_buffer_object *bo,
 			  struct ttm_operation_ctx *ctx)
 {
-	struct ttm_resource *old_mem = &bo->mem;
 	int ret;
 
-	if (old_mem->mem_type == TTM_PL_SYSTEM)
+	if (bo->mem.mem_type == TTM_PL_SYSTEM)
 		return 0;
 
 	ret = ttm_bo_wait_ctx(bo, ctx);
@@ -83,7 +82,6 @@ int ttm_bo_move_to_system(struct ttm_buffer_object *bo,
 
 	ttm_bo_tt_unbind(bo);
 	ttm_resource_free(bo, &bo->mem);
-	old_mem->mem_type = TTM_PL_SYSTEM;
 	return 0;
 }
 EXPORT_SYMBOL(ttm_bo_move_to_system);