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 <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Martin K. Petersen <[e-mail]>

MAINTAINERS

···
 F:	drivers/infiniband/hw/hns/
 
 HISILICON SAS Controller
-M:	John Garry <[e-mail]>
+M:	Xiang Chen <[e-mail]>
 S:	Supported
 W:	http://www.hisilicon.com
 F:	Documentation/devicetree/bindings/scsi/hisilicon-sas.txt