hw/virtio/vhost-vsock: Include missing 'virtio/virtio-bus.h' header

hw/virtio/vhost-vsock: Include missing 'virtio/virtio-bus.h' header

Instead of having "virtio/virtio-bus.h" implicitly included,
explicitly include it, to avoid when rearranging headers:

  hw/virtio/vhost-vsock-common.c: In function ‘vhost_vsock_common_start’:
  hw/virtio/vhost-vsock-common.c:51:5: error: unknown type name ‘VirtioBusClass’; did you mean ‘VirtioDeviceClass’?
     51 |     VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
        |     ^~~~~~~~~~~~~~
        |     VirtioDeviceClass
  hw/virtio/vhost-vsock-common.c:51:25: error: implicit declaration of function ‘VIRTIO_BUS_GET_CLASS’; did you mean ‘VIRTIO_DEVICE_CLASS’? [-Werror=implicit-function-declaration]
     51 |     VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
        |                         ^~~~~~~~~~~~~~~~~~~~
        |                         VIRTIO_DEVICE_CLASS

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20230524093744.88442-8-philmd@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>