When we are renaming a directory to a different directory, we need to
update '..' entry in the moved directory. However nothing prevents moved
directory from being modified and even converted from the in-ICB format
to the normal format which results in a crash. Fix the problem by
locking the moved directory.

Reported-by: syzbot+aebf90eea2671c43112a@syzkaller.appspotmail.com
Signed-off-by: Jan Kara <jack@suse.cz>