RDMA/hns: Use refcount_t APIs for HEM

mainline inclusion
from mainline-v5.12-rc1
commit 82eb481d
category: bugfix
bugzilla: 174002
CVE:NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=82eb481da64586ccd287b2b2c5a086202c65e7eb

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refcount_t is better than integer for reference counting, it will WARN on
overflow/underflow and avoid use-after-free risks.

Link: https://lore.kernel.org/r/1621589395-2435-5-git-send-email-liweihang@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>