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.h b/drivers/gpu/drm/radeon/radeon.h
index f4d1946..f29229c 100644
--- a/drivers/gpu/drm/radeon/radeon.h
+++ b/drivers/gpu/drm/radeon/radeon.h
@@ -261,6 +261,7 @@
 	struct drm_gem_object		*gobj;
 	struct drm_gem_object		gem_base;
 };
+#define gem_to_radeon_bo(gobj) container_of((gobj), struct radeon_bo, gem_base)
 
 struct radeon_bo_list {
 	struct ttm_validate_buffer tv;