Split off diskutil include

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/diskutil.c b/diskutil.c
index 3cbd6fc..cb15882 100644
--- a/diskutil.c
+++ b/diskutil.c
@@ -9,6 +9,7 @@
 
 #include "fio.h"
 #include "smalloc.h"
+#include "diskutil.h"
 
 static int last_majdev, last_mindev;
 static struct disk_util *last_du;