staging: comedi: pcl724: tidy up subdev_8255_init() calls

subdev_8255_init() can fail, make sure to check for it and return
the errno.

The private function subdev_8255_cb() is identical to the default
io callback used by the 8255 driver. Remove it and pass NULL to
subdev_8255_init() so the default callback will be used.

The private function subdev_8255mapped_cb() is used for the memory
memory mapped io of the pet48dio board. Rename this function so
it has namespace associated with the driver.

Casting the iobase passed to subdev_8255_init() is not needed.
Use a local variable for the iobase and remove the casts.

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>