mm/swapfile: fixed the repeated setting logic of memcg_swap_qos_enable

jingdong inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8526M



-----------------------------------------------------

Now when echo 1 > /proc/sys/vm/memcg_swap_qos_enable multiple times,
memcg_swap_qos_reset will be called every time.

In a production environment, when memcg swap qos is working normally,
operations Engineer may execute 'sysctl -p' for other reasons, destroying
the relationship between each container and its corresponding swapfile.

Fixes: eefe54b2 ("memcg: introduce memcg swap qos feature")
Signed-off-by: zhangwei123171 <zhangwei123171@jd.com>
Reviewed-by: zhaoxiaoqiang11 <zhaoxiaoqiang11@jd.com>