mm/memory_hotplug.c: use pfn_to_nid() instead of page_to_nid(pfn_to_page())

Use "pfn_to_nid(pfn)" instead of "page_to_nid(pfn_to_page(pfn))".

Signed-off-by: Xishi Qiu <[e-mail]>
Acked-by: Yasuaki Ishimatsu <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

mm/memory_hotplug.c

···
 	arg.nr_pages = nr_pages;
 	node_states_check_changes_online(nr_pages, zone, &arg);
 
-	nid = page_to_nid(pfn_to_page(pfn));
+	nid = pfn_to_nid(pfn);
 
 	ret = memory_notify(MEM_GOING_ONLINE, &arg);
 	ret = notifier_to_errno(ret);