block: fix warning introduced in efcc7a23

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/block/stream.c b/block/stream.c
index 608a860..8e58322 100644
--- a/block/stream.c
+++ b/block/stream.c
@@ -166,7 +166,7 @@
     BlockDriverState *base = s->base;
     int64_t sector_num, end;
     int ret = 0;
-    int n;
+    int n = 0;
     void *buf;
 
     s->common.len = bdrv_getlength(bs);