vhost/scsi: call vhost_dev_cleanup() at unrealize() time

vhost-scsi calls vhost_dev_init() at realize() time
but forgets to call it's counterpart vhost_dev_cleanup()
at unrealize() time.

Calling it should fix leaking of memory table and
mem_sections table in vhost device. And also unregister
vhost's memory listerner to prevent access from
memory core to freed memory.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <1438262999-287627-1-git-send-email-imammedo@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
