mm/memory_hotplug.c: fix the wrong usage of N_HIGH_MEMORY

In node_states_check_changes_online(), N_HIGH_MEMORY is used to substitute
ZONE_HIGHMEM directly.  This is not right.  N_HIGH_MEMORY is to mark the
memory state of node.  Here zone index is checked, which should be
compared with 'ZONE_HIGHMEM' accordingly.

Replace it with ZONE_HIGHMEM.

This is a code cleanup - no known runtime effects.

Link: http://lkml.kernel.org/r/20190320080732.14933-1-bhe@redhat.com
Fixes: 8efe33f40f ("mm/memory_hotplug.c: simplify node_states_check_changes_online")
Signed-off-by: Baoquan He <bhe@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memory_hotplug.c

@@ -714,7 +714,7 @@ static void node_states_check_changes_online(unsigned long nr_pages,
 	if (zone_idx(zone) <= ZONE_NORMAL && !node_state(nid, N_NORMAL_MEMORY))
 		arg->status_change_nid_normal = nid;
 #ifdef CONFIG_HIGHMEM
-	if (zone_idx(zone) <= N_HIGH_MEMORY && !node_state(nid, N_HIGH_MEMORY))
+	if (zone_idx(zone) <= ZONE_HIGHMEM && !node_state(nid, N_HIGH_MEMORY))
 		arg->status_change_nid_high = nid;
 #endif
 }