scsi: libsas: Delete sas_ata_task.stp_affil_pol

scsi: libsas: Delete sas_ata_task.stp_affil_pol

Since libsas was introduced in commit 2908d778ab3e ("[SCSI] aic94xx: new
driver"), sas_ata_task.stp_affil_pol is never set, so delete it and the
reference in asd_build_ata_ascb().

Signed-off-by: John Garry <john.g.garry@oracle.com>
Link: https://lore.kernel.org/r/20230815115156.343535-10-john.g.garry@oracle.com
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>