staging: comedi: rtd520: use plx register map from plx9080.h

Use the register map defines for the PLX9080 found in plx9080.h
instead of the custom named defines in rtd520.h.

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>