udf: Convert udf_rename() to new directory iteration code

Convert udf_rename() to use new directory iteration code.

Reported-by:  <syzbot+0eaad3590d65102b9391@syzkaller.appspotmail.com>
Reported-by:  <syzbot+b7fc73213bc2361ab650@syzkaller.appspotmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>