memcg: mark memcg1_events static const

Mark memcg1_events static: it's only used by memcontrol.c.  And mark it
const: it's not modified.

Link: http://lkml.kernel.org/r/20180503192940.94971-1-gthelen@google.com
Signed-off-by: Greg Thelen <gthelen@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memcontrol.c

@@ -3083,7 +3083,7 @@ static int memcg_numa_stat_show(struct seq_file *m, void *v)
 #endif /* CONFIG_NUMA */
 
 /* Universal VM events cgroup1 shows, original sort order */
-unsigned int memcg1_events[] = {
+static const unsigned int memcg1_events[] = {
 	PGPGIN,
 	PGPGOUT,
 	PGFAULT,