memory hotplug: fix comments when adding section

Here, pfn_to_node should be page_to_nid.

Link: http://lkml.kernel.org/r/1510735205-22540-1-git-send-email-fan.du@intel.com
Signed-off-by: Fan Du <fan.du@intel.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index fab51a6..c52aa05b 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -265,7 +265,7 @@
 	/*
 	 * Make all the pages reserved so that nobody will stumble over half
 	 * initialized state.
-	 * FIXME: We also have to associate it with a node because pfn_to_node
+	 * FIXME: We also have to associate it with a node because page_to_nid
 	 * relies on having page with the proper node.
 	 */
 	for (i = 0; i < PAGES_PER_SECTION; i++) {