USB: serial: pl2303: add ATEN device ID

Seems that ATEN serial-to-usb devices using pl2303 exist with
different device ids. This patch adds a missing device ID so it
is recognised by the driver.

Signed-off-by: Marcel J.E. Mol <marcel@mesa.nl>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Johan Hovold <johan@kernel.org>