snapshot: fix referencing wrong variable in while loop in do_delvm The while loop variabal is "bs1", but "bs" is always passed to bdrv_snapshot_delete_by_id_or_name. Broken in commit a89d89d, v1.7.0. Signed-off-by: Zhang Haoyu <zhanghy@sangfor.com> Reviewed-by: Markus Armbruster <armbru@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>