MAINTAINERS: Update maintainers for HISILICON ROCE DRIVER

Add myself as a maintainer for HNS RoCE drivers, and update Xavier's
e-amil address.

Link: https://lore.kernel.org/r/1583575114-32194-1-git-send-email-liweihang@huawei.com
Signed-off-by: Weihang Li <liweihang@huawei.com>
Acked-by: Wei Hu (Xavier) <xavier.huwei@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>