Fix disk zone test case

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fio.h b/fio.h
index d84eecf..f2e69a7 100644
--- a/fio.h
+++ b/fio.h
@@ -515,6 +515,7 @@
 	unsigned long io_issues[2];
 	unsigned long long io_blocks[2];
 	unsigned long long io_bytes[2];
+	unsigned long long io_skip_bytes;
 	unsigned long long this_io_bytes[2];
 	unsigned long long zone_bytes;
 	struct fio_sem *mutex;