In several part we still using req->dev or VIRTIO_DEVICE(req->dev)
when we have already defined s and vdev pointers:
    VirtIOBlock *s = req->dev;
    VirtIODevice *vdev = VIRTIO_DEVICE(s);

Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Liam Merwick <liam.merwick@oracle.com>
Message-id: 20190208142347.214815-1-sgarzare@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>