RDMA/hns: Remove redundant memcpy()

srq_context is a local variables and is only used to get some fields from
buffer of mailbox. It's meaningless to copy mailbox's buffer's contents
back to it.

Link: https://lore.kernel.org/r/1588931159-56875-8-git-send-email-liweihang@huawei.com


Signed-off-by: Weihang Li <liweihang@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>