USB: serial: metro-usb: add MS7820 device id

Add device-id entry for (Honeywell) Metrologic MS7820 bar code scanner.

The device has two interfaces (in this mode?); a vendor-specific
interface with two interrupt endpoints and a second HID interface, which
we do not bind to.

Reported-by: Ladislav Dobrovsky <ladislav.dobrovsky@gmail.com>
Tested-by: Ladislav Dobrovsky <ladislav.dobrovsky@gmail.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Johan Hovold <johan@kernel.org>