staging: comedi: ni_labpc: fix 8255 dio subdevice init

The subdev_8255_init() function can fail. Check for failure and
return the errno.

Consolidate the mmio/ioport calls to subdev_8255_init(). The callback
function can be added with a simple ? : test and the cast of the iobase
is not necessary.

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