tools/virtio: fix virtio_test execution

virtio_test hangs on __vring_new_virtqueue() because `vqs_list_lock`
is not initialized.

Let's initialize it in vdev_info_init().

Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Link: https://lore.kernel.org/r/20220118150631.167015-1-sgarzare@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>