staging: comedi: ni_65xx: cleanup recurring register map

Convert the inline functions used to calculate the offsets to the
recurring port registers and rename them to remove the CamelCase.

Define all the recurring registers.

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>