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_device.c b/drivers/gpu/drm/radeon/radeon_device.c
index 13945bd..7c0a3f2 100644
--- a/drivers/gpu/drm/radeon/radeon_device.c
+++ b/drivers/gpu/drm/radeon/radeon_device.c
@@ -860,7 +860,7 @@
 		if (rfb == NULL || rfb->obj == NULL) {
 			continue;
 		}
-		robj = rfb->obj->driver_private;
+		robj = gem_to_radeon_bo(rfb->obj);
 		/* don't unpin kernel fb objects */
 		if (!radeon_fbdev_robj_is_fb(rdev, robj)) {
 			r = radeon_bo_reserve(robj, false);