staging: comedi: 8255: add a comedi_device param to the (*io) callback

The 8255 driver uses an (*io) callback to read/write the registers
of the 8255 device. The default callback provided by the driver uses
inb()/outb() calls to access to registers based on an 'iobase' that
was initialized during the subdev_8255_init() and a 'port' value.

The users of this module can optionally provide a custom (*io) callback
to handle the read/write in another manner.

Make the (*io) callback a bit more flexible by also passing the
comedi_device pointer as a parameter.

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