Revert "virtio: use virtio_device_ready() in virtio_device_restore()"

This reverts commit 8d65bc9a

.

We reverted the problematic changes, no more need for work
arounds on restore.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>