scsi: target: vhost-scsi: Use LIO wq cmd submission helper

Convert vhost-scsi to use the LIO wq cmd submission helper.

Link: https://lore.kernel.org/r/20210227170006.5077-18-michael.christie@oracle.com
Signed-off-by: Mike Christie <michael.christie@oracle.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>