virtio serial port: fix to incomplete QOMify Signed-off-by: Cao jin <caoj.fnst@cn.fujitsu.com> Message-Id: <1452068575-21543-1-git-send-email-caoj.fnst@cn.fujitsu.com> Reviewed-by: Amit Shah <amit.shah@redhat.com> Signed-off-by: Amit Shah <amit.shah@redhat.com>