mm/damon/sysfs-schemes: hold damon_sysfs_lock in target_metric_store()

[mm/damon/sysfs-schemes: hold damon_sysfs_lock in target_metric_store()] damon_sysfs_add_quota_score() reads damos_sysfs_quota_goal->metric twice, once to set damos_quota_goal->metric to the value, an