RDMA/hns: Delete redundant judgment when preparing descriptors

There is no need to use a for loop to assign values for an array of cmd
descriptors which has only two elements.

Link: https://lore.kernel.org/r/1612517974-31867-13-git-send-email-liweihang@huawei.com


Signed-off-by: Xinhao Liu <liuxinhao5@hisilicon.com>
Signed-off-by: Weihang Li <liweihang@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>