RDMA/hns: Repacing 'dseg_len' by macros in fill_ext_sge_inl_data()

The sge size is known to be constant, so it's unnecessary to use sizeof to
calculate.

Link: https://lore.kernel.org/r/20220922123315.3732205-11-xuhaoyue1@hisilicon.com


Signed-off-by: Luoyouming <luoyouming@huawei.com>
Signed-off-by: Haoyue Xu <xuhaoyue1@hisilicon.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>