scsi: hisi_sas: make local symbol host_attrs static

Fixes the following sparse warning:

drivers/scsi/hisi_sas/hisi_sas_main.c:1691:25: warning:
 symbol 'host_attrs' was not declared. Should it be static?

Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Acked-by: John Garry <john.garry@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>