Btrfs: include vmalloc.h in check-integrity.c

Fengguang's build monster reported warnings on some arches because we
don't have vmalloc.h included
Signed-off-by: Chris Mason <clm@fb.com>
Reported-by: fengguang.wu@intel.com

fs/btrfs/check-integrity.c

@@ -94,6 +94,7 @@
 #include <linux/mutex.h>
 #include <linux/genhd.h>
 #include <linux/blkdev.h>
+#include <linux/vmalloc.h>
 #include "ctree.h"
 #include "disk-io.h"
 #include "hash.h"