memcg: Fix the problem of cat memory.high_async_ratio

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4IMAK


CVE: NA

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The patch fixes the problem of cat memory.high_async_ratio.
After this patch, when user cat memory.high_async_ratio, the correct
memory.high_async_ratio will be shown.

Show case:
/sys/fs/cgroup/test # cat memory.high_async_ratio
0
/sys/fs/cgroup/test # echo 90 > memory.high_async_ratio
/sys/fs/cgroup/test # cat memory.high_async_ratio
90
/sys/fs/cgroup/test # echo 85 > memory.high_async_ratio
/sys/fs/cgroup/test # cat memory.high_async_ratio
85

Signed-off-by: Lu Jialin <lujialin4@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>