scsi: hisi_sas: Don't bother clearing status buffer IU in task prep

For struct hisi_sas_status_buffer, it contains struct hisi_sas_err_record
and iu[1024]. The struct iu[1024] will be filled fully by the response of
disks, so it is not need to initialize them to 0, but for the struct
hisi_sas_err_record, SAS controller only fill some fields of
hisi_sas_err_record according to hw designer, so it should be initialised
to 0.  After the change, cpu utilization percentage of memset() is changed
from 1.7% to 0.12%.
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

@@ -545,7 +545,8 @@ static int hisi_sas_task_prep(struct sas_task *task,
 
 	memset(slot->cmd_hdr, 0, sizeof(struct hisi_sas_cmd_hdr));
 	memset(hisi_sas_cmd_hdr_addr_mem(slot), 0, HISI_SAS_COMMAND_TABLE_SZ);
-	memset(hisi_sas_status_buf_addr_mem(slot), 0, HISI_SAS_STATUS_BUF_SZ);
+	memset(hisi_sas_status_buf_addr_mem(slot), 0,
+	       sizeof(struct hisi_sas_err_record));
 
 	switch (task->task_proto) {
 	case SAS_PROTOCOL_SMP:
@@ -2005,7 +2006,8 @@ hisi_sas_internal_abort_task_exec(struct hisi_hba *hisi_hba, int device_id,
 
 	memset(slot->cmd_hdr, 0, sizeof(struct hisi_sas_cmd_hdr));
 	memset(hisi_sas_cmd_hdr_addr_mem(slot), 0, HISI_SAS_COMMAND_TABLE_SZ);
-	memset(hisi_sas_status_buf_addr_mem(slot), 0, HISI_SAS_STATUS_BUF_SZ);
+	memset(hisi_sas_status_buf_addr_mem(slot), 0,
+	       sizeof(struct hisi_sas_err_record));
 
 	hisi_sas_task_prep_abort(hisi_hba, slot, device_id,
 				      abort_flag, task_tag);