let __dec_zone_page_state use __dec_zone_state

This removes code duplication and makes __dec_zone_page_state look like
__inc_zone_page_state.

Signed-off-by: Uwe Kleine-König <Uwe.Kleine-Koenig@digi.com>
Acked-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/vmstat.h

@@ -246,8 +246,7 @@ static inline void __dec_zone_state(struct zone *zone, enum zone_stat_item item)
 static inline void __dec_zone_page_state(struct page *page,
 			enum zone_stat_item item)
 {
-	atomic_long_dec(&page_zone(page)->vm_stat[item]);
-	atomic_long_dec(&vm_stat[item]);
+	__dec_zone_state(page_zone(page), item);
 }
 
 /*