staging: comedi: cb_pcidas: tidy up PCI BAR4 register defines

Convert the inline function DAC_DATA_REG() into a simple macro.

Rename the defines for the PCI BAR4 register offsets so they have
namespace associated with the driver and convert the offsets to
hex.

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>