vhost-scsi: adjust vhost_scsi_get_desc() to log vring descriptors

vhost-scsi: adjust vhost_scsi_get_desc() to log vring descriptors

Adjust vhost_scsi_get_desc() to facilitate logging of vring descriptors.

Add new arguments to allow passing the log buffer and length to
vhost_get_vq_desc().

In addition, reset 'log_num' since vhost_get_vq_desc() may reset it only
after certain condition checks.

Suggested-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Reviewed-by: Mike Christie <michael.christie@oracle.com>
Message-Id: <20250403063028.16045-6-dongli.zhang@oracle.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>