RDMA/hns: Redefine the member of hns_roce_cq struct

RDMA/hns: Redefine the member of hns_roce_cq struct

There is no need to package buf and mtt into hns_roce_cq_buf, which will
make code more complex, just delete this struct and move buf and mtt into
hns_roce_cq. Furthermore, we add size member for hns_roce_buf to avoid
repeatly calculating where needed it.

Link: https://lore.kernel.org/r/1574044493-46984-3-git-send-email-liweihang@hisilicon.com
Signed-off-by: Yixian Liu <liuyixian@huawei.com>
Signed-off-by: Weihang Li <liweihang@hisilicon.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>