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>

arch/powerpc/mm/numa.c

@@ -938,8 +938,7 @@ static void __init mark_reserved_regions_for_nid(int nid)
 		unsigned long start_pfn = physbase >> PAGE_SHIFT;
 		unsigned long end_pfn = PFN_UP(physbase + size);
 		struct node_active_region node_ar;
-		unsigned long node_end_pfn = node->node_start_pfn +
-					     node->node_spanned_pages;
+		unsigned long node_end_pfn = pgdat_end_pfn(node);
 
 		/*
 		 * Check to make sure that this memblock.reserved area is