RDMA/hns: Remove unnecessary flush operation for workqueue

mainline inclusion
from mainline-v5.12-rc1
commit dc1d06e6
category: bugfix
bugzilla: 174002
CVE:NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=dc1d06e699b5fe58f97df7123996ba8556b386c9

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As a flush operation is implemented inside destroy_workqueue(), there is
no need to do flush operation before.

Fixes: bfcc681b ("IB/hns: Fix the bug when free mr")
Fixes: 0425e3e6 ("RDMA/hns: Support flush cqe for hip08 in kernel space")
Link: https://lore.kernel.org/r/1618305087-30799-1-git-send-email-liweihang@huawei.com


Signed-off-by: Yixian Liu <liuyixian@huawei.com>
Signed-off-by: Weihang Li <liweihang@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: wangsirong <wangsirong@huawei.com>
Reviewed-by: ChunZhi Hu <huchunzhi@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>