virtio-serial: don't migrate the config space

virtio-serial: don't migrate the config space

The device configuration is set at realize time and never changes. It
should not be migrated as it is done today. For the sake of compatibility,
let's just skip them at load time.

Signed-off-by: Alexander Graf <agraf@suse.de>
[ added missing casts to uint16_t *,
  added From, SoB and commit message,
  Greg Kurz <gkurz@linux.vnet.ibm.com> ]
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
(cherry picked from commit e38e943a1fa20d04deb1899be19b12aadec7a585)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>