drm/nouveau: clean up nouveau_bo_move_ntfy

Just another leftover from a TTM cleanup.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210315191432.153826-2-christian.koenig@amd.com