staging: comedi: pass usb interface to comedi_usb_auto_config

The comedi_usb_auto_config() and comedi_usb_auto_unconfig() functions
currently take a 'struct usb_device *'.  It makes more sense to pass a
'struct usb_interface *' to allow for composite USB devices.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>