block: Convert first_drv to QLIST

Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/block_int.h b/block_int.h
index 466a38c..d4067ff 100644
--- a/block_int.h
+++ b/block_int.h
@@ -126,7 +126,7 @@
     /* Set if newly created images are not guaranteed to contain only zeros */
     int no_zero_init;
 
-    struct BlockDriver *next;
+    QLIST_ENTRY(BlockDriver) list;
 };
 
 struct BlockDriverState {