vl: free err

err is not freed after use, thus causing memory leak. This patch fixes
it.

Signed-off-by: Hu Tao <hutao@cn.fujitsu.com>
Cc: qemu-trivial@nongnu.org
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

vl.c

@@ -2918,6 +2918,7 @@ out:
     g_free(dummy);
     if (err) {
         qerror_report_err(err);
+        error_free(err);
         return -1;
     }
     return 0;