staging: comedi: adv_pci1723: tidy up register map

For aesthetics, rename the defines used for the register map offsets and
remove the unnecessary comments. Add the bit defines for the 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>