builtin/update-index.c: prefer "err" to "errno" in process_lstat_error

"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>

builtin/update-index.c

@@ -255,7 +255,7 @@ static int process_lstat_error(const char *path, int err)
 {
 	if (err == ENOENT || err == ENOTDIR)
 		return remove_one_path(path);
-	return error("lstat(\"%s\"): %s", path, strerror(errno));
+	return error("lstat(\"%s\"): %s", path, strerror(err));
 }
 
 static int add_one_path(const struct cache_entry *old, const char *path, int len, struct stat *st)