Fix disk utilization and ioscheduler switch on raw devices

Add a method for mapping a raw device to the real block device,
so our sysfs lookup stuff works as expected.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fio.h b/fio.h
index 07b40ff..a86a582 100644
--- a/fio.h
+++ b/fio.h
@@ -648,7 +648,7 @@
 
 	char *name;
 	char path[256];
-	dev_t dev;
+	int major, minor;
 
 	struct disk_util_stat dus;
 	struct disk_util_stat last_dus;