"errno" is already passed in as "err". Here we should use err instead of
errno. errno is probably a copy/paste mistake in e011054 (Teach
git-update-index about gitlinks - 2007-04-12)
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>