scsi: libsas: Simplify the return expression of sas_discover_* functions

Simplify the return expression.

Link: https://lore.kernel.org/r/20200921134558.3478922-1-liushixin2@huawei.com


Reviewed-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Liu Shixin <liushixin2@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>