Fix migration for ide devices

commit 93c8cfd9
Author: Gleb Natapov <gleb@redhat.com>
Date:   Sun Aug 2 11:36:47 2009 +0300

    make windows notice media change

Broke save/restore by loading a new field but not saving it.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>