qemu-img: Release reference to BlockDriverState

Signed-off-by: Prasad Joshi <prasadjoshi.linux@gmail.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

qemu-img.c

diff --git a/qemu-img.c b/qemu-img.c
index 77d946b..8455994 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -1809,6 +1809,7 @@
         if (err) {
             error_report("%s", error_get_pretty(err));
             error_free(err);
+            bdrv_unref(bs);
             goto err;
         }