USB: serial: pl2303: add Allied Telesis VT-Kit3

This is adds the vendor and device id for the AT-VT-Kit3 which is a
pl2303-based device.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Johan Hovold <johan@kernel.org>