vhost scsi: Convert to SPDX identifier

use SPDX-License-Identifier instead of a verbose license text

Signed-off-by: Cai Huoqing <caihuoqing@baidu.com>
Link: https://lore.kernel.org/r/20210821123320.734-1-caihuoqing@baidu.com


Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>