drm/cirrus: remove unused driver_private access

gem_bo->driver_private is never read by cirrus nor DRM core. No need to
set it. Besides, drm core clears it during setup, anyway.
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/cirrus/cirrus_ttm.c

@@ -326,7 +326,6 @@ int cirrus_bo_create(struct drm_device *dev, int size, int align,
 		return ret;
 	}
 
-	cirrusbo->gem.driver_private = NULL;
 	cirrusbo->bo.bdev = &cirrus->ttm.bdev;
 
 	cirrus_ttm_placement(cirrusbo, TTM_PL_FLAG_VRAM | TTM_PL_FLAG_SYSTEM);