!5485 nfsd: fix use-after-free due to delegation race

Merge Pull Request from: @ci-robot 
 
PR sync from: Li Lingfeng <lilingfeng3@huawei.com>
https://mailweb.openeuler.org/hyperkitty/list/kernel@openeuler.org/message/5K7LBT6L442VSYUU7P5A5KQ4VUCNLGFI/ 
 
https://gitee.com/openeuler/kernel/issues/I99EU2 
 
Link:https://gitee.com/openeuler/kernel/pulls/5485

 

Reviewed-by: Liu YongQiang <liuyongqiang13@huawei.com>
Signed-off-by: Zhang Changzhong <zhangchangzhong@huawei.com>