mm: memcontrol: drop superfluous entry in the per-memcg stats array

MEM_CGROUP_STAT_NSTATS is just a delimiter for cgroup1 statistics, not
an actual array entry.  Reuse it for the first cgroup2 stat entry, like
in the event array.

Fixes: b2807f0 ("mm: memcontrol: add "sock" to cgroup2 memory.stat")
Signed-off-by: Johannes Weiner <[email protected]>
Cc: Vladimir Davydov <[email protected]>
Cc: Michal Hocko <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: hnaz

include/linux/memcontrol.h

@@ -51,7 +51,7 @@ enum mem_cgroup_stat_index {
 	MEM_CGROUP_STAT_SWAP,		/* # of pages, swapped out */
 	MEM_CGROUP_STAT_NSTATS,
 	/* default hierarchy stats */
-	MEMCG_SOCK,
+	MEMCG_SOCK = MEM_CGROUP_STAT_NSTATS,
 	MEMCG_NR_STAT,
 };