staging: comedi: addi_apci_16xx: rewrite low-level support code

The current low-level support code in hwdrv_apci16xx.c is seriously
broken. Besides that, it's overly complicated.

Rewrite, and simplify, the low-level code so it complies with the
comedi API.

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>