As it's only used inside hw/virtio/vhost-vdpa.c.

Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
Message-Id: <20210413133737.1574-1-yuzenghui@huawei.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>