mm/vmstat.c: proper externs

This patch adds proper extern declarations for five variables in
include/linux/vmstat.h

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/vmstat.c b/mm/vmstat.c
index c3d4a78..b0d08e6 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -13,6 +13,7 @@
 #include <linux/err.h>
 #include <linux/module.h>
 #include <linux/cpu.h>
+#include <linux/vmstat.h>
 #include <linux/sched.h>
 
 #ifdef CONFIG_VM_EVENT_COUNTERS