staging: comedi: hwdrv_apci3120: clean up comments

This patch fixes improper comment indentation, removes dead code and
obsolete comments, and conforms remaining comments to a consistent kernel
commenting style.
Signed-off-by: Chase Southwood <chase.southwood@gmail.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Cc: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>