mm: use pgdat_end_pfn() to simplify the code in others

Use "pgdat_end_pfn()" instead of "pgdat->node_start_pfn +
pgdat->node_spanned_pages".  Simplify the code, no functional change.

Signed-off-by: Xishi Qiu <qiuxishi@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
index 06ea155..5ed0e52 100644
--- a/fs/proc/kcore.c
+++ b/fs/proc/kcore.c
@@ -255,8 +255,7 @@
 	end_pfn = 0;
 	for_each_node_state(nid, N_MEMORY) {
 		unsigned long node_end;
-		node_end  = NODE_DATA(nid)->node_start_pfn +
-			NODE_DATA(nid)->node_spanned_pages;
+		node_end = node_end_pfn(nid);
 		if (end_pfn < node_end)
 			end_pfn = node_end;
 	}