RDMA/hns: Remove useless NULL check in hns_roce_get_netdev()

driver inclusion
category: cleanup
bugzilla: https://gitee.com/openeuler/kernel/issues/I8LY0D



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This patch removes an unnecessary NULL check for ndev in
hns_roce_get_netdev().

Signed-off-by: Chengchang Tang <tangchengchang@huawei.com>