tools/virtio: initialize spinlocks in vring_test.c

The virtio_device vqs_list spinlocks must be initialized before use to
prevent functions that manipulate the device virtualqueues, such as
vring_new_virtqueue(), from blocking indefinitely.

Signed-off-by: Ricardo Cañuelo <ricardo.canuelo@collabora.com>
Message-Id: <20221012062949.1526176-1-ricardo.canuelo@collabora.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>