staging: comedi: 8255.h: don't include "../comedidev.h"

The Comedi "8255.h" header doesn't use anything from "comedidev.h" apart
from `struct comedi_device` and `struct comedi_subdevice`, which are
only used to construct corresponding pointer types within the parameter
lists of function prototypes.  Just declare those structure types
incompletely and don't bother including "comedidev.h".

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>