parport_open — find a device by canonical device number
| struct pardevice * parport_open ( | int devnum, | 
| const char * name ); | 
   This function is similar to parport_register_device, except
   that it locates a device by its number rather than by the port
   it is attached to.
   
   All parameters except for devnum are the same as for
   parport_register_device.  The return value is the same as
   for parport_register_device.