scsi: hisi_sas: fix dma_unmap_sg() parameter

For function dma_unmap_sg(), the <nents> parameter should be number of
elements in the scatterlist prior to the mapping, not after the mapping.

Fix this usage.
Signed-off-by: NXiang Chen <chenxiang66@hisilicon.com>
Signed-off-by: NJohn Garry <john.garry@huawei.com>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/hisi_sas/hisi_sas_main.c

@@ -192,7 +192,8 @@ void hisi_sas_slot_task_free(struct hisi_hba *hisi_hba, struct sas_task *task,
 
 		if (!sas_protocol_ata(task->task_proto))
 			if (slot->n_elem)
-				dma_unmap_sg(dev, task->scatter, slot->n_elem,
+				dma_unmap_sg(dev, task->scatter,
+					     task->num_scatter,
 					     task->data_dir);
 
 		if (sas_dev)
@@ -431,7 +432,8 @@ static int hisi_sas_task_prep(struct sas_task *task, struct hisi_sas_dq
 	dev_err(dev, "task prep: failed[%d]!\n", rc);
 	if (!sas_protocol_ata(task->task_proto))
 		if (n_elem)
-			dma_unmap_sg(dev, task->scatter, n_elem,
+			dma_unmap_sg(dev, task->scatter,
+				     task->num_scatter,
 				     task->data_dir);
 prep_out:
 	return rc;