RDMA/hns: Refactor code about SRQ Context

Reduce parameter numbers of write_srqc() and move some related code into
it from alloc_srqc().

Link: https://lore.kernel.org/r/1611997090-48820-8-git-send-email-liweihang@huawei.com


Signed-off-by: Wenpeng Liang <liangwenpeng@huawei.com>
Signed-off-by: Weihang Li <liweihang@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>