bridge: No QoS configured is not an error

If no QoS is configured, type value is likely to be an empty
string.

This is not an error though, so use the regular command reply
function, not the error one.

For example, before this patch:
  # ovs-appctl -t ovs-vswitchd qos/show vhost-user1
  QoS not configured on vhost-user1
  ovs-appctl: ovs-vswitchd: server returned an error

After the patch:
  # ovs-appctl -t ovs-vswitchd qos/show vhost-user1
  QoS not configured on vhost-user1

Signed-off-by: Maxime Coquelin <[email protected]>
Acked-by: Ian Stokes <[email protected]>
Acked-by: Daniele Di Proietto <[email protected]>

vswitchd/bridge.c

@@ -3199,7 +3199,7 @@ qos_unixctl_show(struct unixctl_conn *conn, int argc OVS_UNUSED,
             unixctl_command_reply(conn, ds_cstr(&ds));
         } else {
             ds_put_format(&ds, "QoS not configured on %s\n", iface->name);
-            unixctl_command_reply_error(conn, ds_cstr(&ds));
+            unixctl_command_reply(conn, ds_cstr(&ds));
         }
     } else {
         ds_put_format(&ds, "%s: failed to retrieve QOS configuration (%s)\n",