RDMA/hns: Alloc MTR memory before alloc_mtt()

driver inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5Y79T



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MTR memory allocation do not depend on allocation of MTT. And MTT
allocation can be adjusted according to MTR, so make MTR allocation
before MTT allocation.

Signed-off-by: Chengchang Tang <tangchengchang@huawei.com>
Reviewed-by: Yangyang Li <liyangyang20@huawei.com>
Reviewed-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>