scsi: hisi_sas: Reduce HISI_SAS_SGE_PAGE_CNT in size

Macro HISI_SAS_SGE_PAGE_CNT is defined to SG_CHUNK_SIZE, which is 128.

This means that sizeof(struct hisi_sas_slot_buf_table) is 4192. This is
just over a 4K, which can mean inefficient DMA memory usage (for no PI).

Reduce the size of HISI_SAS_SGE_PAGE_CNT to 124 to fit in a 4K page. With
this change, we experience no performance hit.

Cc: dann frazier <dann.frazier@canonical.com>
Signed-off-by: John Garry <john.garry@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>