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

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>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: "Luck, Tony" <tony.luck@intel.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/sh/mm/init.c b/arch/sh/mm/init.c
index 33890fd..2d089fe 100644
--- a/arch/sh/mm/init.c
+++ b/arch/sh/mm/init.c
@@ -231,7 +231,7 @@
 	if (!p->node_spanned_pages)
 		return;
 
-	end_pfn = p->node_start_pfn + p->node_spanned_pages;
+	end_pfn = pgdat_end_pfn(p);
 
 	total_pages = bootmem_bootmap_pages(p->node_spanned_pages);