hw/audio/virtio-sound: mark the device as unmigratable

hw/audio/virtio-sound: mark the device as unmigratable

The virtio-sound device is currently not migratable. QEMU crashes
on the source machine at some point during the migration with a
segmentation fault.

Even with this bug fixed, the virtio-sound device doesn't migrate
the state of the audio streams. For example, running streams leave
the device on the destination machine in a broken condition.

Mark the device as unmigratable until these issues have been fixed.

Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20231204072837.6058-1-vr_qemu@t-online.de>