scsi: hisi_sas: use dma_zalloc_coherent()

This is a warning coming from Coccinelle, and need to use new interface
dma_zalloc_coherent() instead of dma_alloc_coherent()/memset().

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>