usb: usb251xb: Add USB2517 LED settings

USB2517 supports two LED modes: USB mode and speed (default) indication
mode. The last one can be switched on by corresponding dts property.
Since USB251xb hubs doesn't support LEDs settings, we need to ignore
this setting.

Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>