vqs are freed in virtscsi_freeze but the hotcpu_notifier is not
unregistered. We will have a use-after-free usage when the notifier
callback is called after virtscsi_freeze.

Fixes: 285e71ea
("virtio-scsi: reset virtqueue affinity when doing cpu hotplug")

Cc: stable@vger.kernel.org
Signed-off-by: NAsias He <asias.hejun@gmail.com>
Reviewed-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NJason Wang <jasowang@redhat.com>
Signed-off-by: NRusty Russell <rusty@rustcorp.com.au>