staging: comedi: cb_pcimdda: cleanup the 8255 subdevice init

The dio_registers variable in the private data is only used to
pass the base address to the 8255 subdevice. Remove the variable
from the private data and pass the value directly to the
subdev_8255_init() function.

Make sure to check the return from subdev_8255_init(). That
function can fail. For aesthetic reasons, rename the local
variable 'err' to 'ret'.

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