scsi: MAINTAINERS: Make Xiang Chen HiSilicon SAS controller driver maintainer

scsi: MAINTAINERS: Make Xiang Chen HiSilicon SAS controller driver maintainer

I am soon leaving Huawei, so will no longer maintain this driver. However I
will stay active in upstream Linux storage domain.

Xiang Chen has worked on the driver for as long as I have and has good
knowledge of the driver, so should do a good job.

Signed-off-by: John Garry <john.garry@huawei.com>
Link: https://lore.kernel.org/r/1666784008-125519-1-git-send-email-john.garry@huawei.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>