drm/ttm: refine ghost BO resv criteria

Ghost BOs need to stick with the resv object only when the origin is imported.

This is a low hanging fruit to avoid OOM situations on evictions.
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: xinhui pan <xinhui.pan@amd.com>
Link: https://patchwork.freedesktop.org/patch/352740/

drivers/gpu/drm/ttm/ttm_bo_util.c

@@ -511,7 +511,7 @@ static int ttm_buffer_object_transfer(struct ttm_buffer_object *bo,
 	kref_init(&fbo->base.kref);
 	fbo->base.destroy = &ttm_transfered_destroy;
 	fbo->base.acc_size = 0;
-	if (bo->base.resv == &bo->base._resv)
+	if (bo->type != ttm_bo_type_sg)
 		fbo->base.base.resv = &fbo->base.base._resv;
 
 	dma_resv_init(&fbo->base.base._resv);