staging: comedi: daqboard2000: rename acq status register macros

Rename the macros associated with the acquisition status register to
avoid CamelCase and to make it clear which register they are associated
with.

Add a macro to define the offset of the read-only acquisition status
register.  It's the same offset as the acquisition control register,
which is write-only.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>