staging: comedi: 8255_pci: tidy up pci_8255_mmio()

The 8255 driver (*io) callback now includes the comedi_device pointer.
Using this we can get the ioremap'ed base address.

Instead of passing the (cast) mmio address to subdev_8255_init(), pass
the 'iobase' of the 8255 registers (i * 4).

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>