usb: serial: mos7840: Add USB ID to support the B&B Electronics USOPTL4-2P.

Add the USB ID needed to support B&B Electronic's 2-port, optically-isolated,
powered, USB to RS485 converter.

Signed-off-by: Dave Ludlow <dave.ludlow@bay.ws>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>