block/win32: fix 'ret not initialized' warning

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Stefan Weil <sw@weilnetz.de>
Reviewed-by: Fam Zheng <famz@redhat.com>
Message-id: 20170516074256.24731-1-kraxel@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

block/file-win32.c

@@ -346,6 +346,7 @@ static int raw_open(BlockDriverState *bs, QDict *options, int flags,
 
     if (qdict_get_try_bool(options, "locking", false)) {
         error_setg(errp, "locking=on is not supported on Windows");
+        ret = -EINVAL;
         goto fail;
     }