RDMA/hns: Remove unnecessary checks for NULL in mtr_alloc_bufs()

ib_umem_get() never return NULL.

Fixes: 3c873161 ("RDMA/hns: Add support for addressing when hopnum is 0")
Signed-off-by: Chengchang Tang <tangchengchang@huawei.com>
Signed-off-by: Junxian Huang <huangjunxian6@hisilicon.com>
Link: https://lore.kernel.org/r/20231207114231.2872104-5-huangjunxian6@hisilicon.com


Signed-off-by: Leon Romanovsky <leon@kernel.org>