mm: use zone_end_pfn() instead of zone_start_pfn+spanned_pages

Use "zone_end_pfn()" instead of "zone->zone_start_pfn + zone->spanned_pages".
Simplify the code, no functional change.

[akpm@linux-foundation.org: fix build]
Signed-off-by: Xishi Qiu <qiuxishi@huawei.com>
Cc: Cody P Schafer <cody@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memory_hotplug.c

@@ -229,7 +229,7 @@ static void grow_zone_span(struct zone *zone, unsigned long start_pfn,
 
 	zone_span_writelock(zone);
 
-	old_zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages;
+	old_zone_end_pfn = zone_end_pfn(zone);
 	if (!zone->spanned_pages || start_pfn < zone->zone_start_pfn)
 		zone->zone_start_pfn = start_pfn;
 
@@ -514,8 +514,9 @@ static int find_biggest_section_pfn(int nid, struct zone *zone,
 static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
 			     unsigned long end_pfn)
 {
-	unsigned long zone_start_pfn =  zone->zone_start_pfn;
-	unsigned long zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages;
+	unsigned long zone_start_pfn = zone->zone_start_pfn;
+	unsigned long z = zone_end_pfn(zone); /* zone_end_pfn namespace clash */
+	unsigned long zone_end_pfn = z;
 	unsigned long pfn;
 	struct mem_section *ms;
 	int nid = zone_to_nid(zone);