Only check FIO_DISKLESSIO in stat.c

Just make the null engine set that flag as well.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/stat.c b/stat.c
index ec418da..0ecc164 100644
--- a/stat.c
+++ b/stat.c
@@ -246,7 +246,7 @@
 	dev_t dev;
 	char *p;
 
-	if (!td->do_disk_util || (td->io_ops->flags & (FIO_DISKLESSIO | FIO_NULLIO)))
+	if (!td->do_disk_util || (td->io_ops->flags & FIO_DISKLESSIO))
 		return;
 
 	/*