scsi: libsas: Make sas_{alloc, alloc_slow, free}_task() private

We have no users outside libsas any longer, so make sas_alloc_task(),
sas_alloc_slow_task(), and sas_free_task() private.

Signed-off-by: John Garry <john.garry@huawei.com>
Link: https://lore.kernel.org/r/1665998435-199946-8-git-send-email-john.garry@huawei.com


Tested-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Tested-by: Niklas Cassel <niklas.cassel@wdc.com> # pm80xx
Reviewed-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>