USB: ftdi driver pid for dmx-interfaces

Please add a usb pid to the ftdi_sio driver. The pid is used by dmx4all
dmx-interfaces (for stage lighting).

The interfaces are using the usb-id 0403:c850. I added the id to the driver
and it works perfectly. I added a patch for linux 2.6.18.1, too.

From: Frank Sievertsen <frank@sievertsen.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>