drm/radeon: introduce gem_to_radeon_bo helper

... and switch it to container_of upcasting.

v2: converted new pageflip code-paths.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/radeon/radeon_object.c b/drivers/gpu/drm/radeon/radeon_object.c
index 9324c88..2be1896 100644
--- a/drivers/gpu/drm/radeon/radeon_object.c
+++ b/drivers/gpu/drm/radeon/radeon_object.c
@@ -128,7 +128,7 @@
 	}
 	bo->rdev = rdev;
 	bo->gobj = &bo->gem_base;
-	bo->gem_base.driver_private = bo;
+	bo->gem_base.driver_private = NULL;
 	bo->surface_reg = -1;
 	INIT_LIST_HEAD(&bo->list);
 	radeon_ttm_placement_from_domain(bo, domain);
@@ -282,7 +282,6 @@
 		list_del_init(&bo->list);
 		mutex_unlock(&bo->rdev->gem.mutex);
 		radeon_bo_unref(&bo);
-		gobj->driver_private = NULL;
 		drm_gem_object_unreference(gobj);
 		mutex_unlock(&rdev->ddev->struct_mutex);
 	}