hugetlb_cgroup: fix wrong hugetlb cgroup numa stat

We forget to set cft->private for numa stat file.  As a result, numa stat
of hstates[0] is always showed for all hstates.  Encode the hstates index
into cft->private to fix this issue.

Link: https://lkml.kernel.org/r/20220723073804.53035-1-linmiaohe@huawei.com
Fixes: f477619 ("hugetlb: add hugetlb.*.numa_stat file")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Acked-by: Muchun Song <songmuchun@bytedance.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/hugetlb_cgroup.c

@@ -772,6 +772,7 @@ static void __init __hugetlb_cgroup_file_dfl_init(int idx)
 	/* Add the numa stat file */
 	cft = &h->cgroup_files_dfl[6];
 	snprintf(cft->name, MAX_CFTYPE_NAME, "%s.numa_stat", buf);
+	cft->private = MEMFILE_PRIVATE(idx, 0);
 	cft->seq_show = hugetlb_cgroup_read_numa_stat;
 	cft->flags = CFTYPE_NOT_ON_ROOT;