scsi: hisi_sas: Make slot buf minimum allocation of PAGE_SIZE

For a system with PAGE_SIZE of 16K or 64K, the size every time we want to
alloc may be small like 4K, but for function dmam_alloc_coherent(), the
least size it allocates is PAGE_SIZE, so it will waste much memory for the
situation.

To solve the issue, limit the minimum allocation size of slot buf to
PAGE_SIZE.
Signed-off-by: Xiang Chen <chenxiang66@hisilicon.com>
Signed-off-by: John Garry <john.garry@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/hisi_sas/hisi_sas_main.c

@@ -2389,7 +2389,7 @@ int hisi_sas_alloc(struct hisi_hba *hisi_hba)
 	else
 		sz_slot_buf_ru = sizeof(struct hisi_sas_slot_buf_table);
 	sz_slot_buf_ru = roundup(sz_slot_buf_ru, 64);
-	s = lcm(max_command_entries_ru, sz_slot_buf_ru);
+	s = max(lcm(max_command_entries_ru, sz_slot_buf_ru), PAGE_SIZE);
 	blk_cnt = (max_command_entries_ru * sz_slot_buf_ru) / s;
 	slots_per_blk = s / sz_slot_buf_ru;