staging: comedi: das16: tidy up the register map defines

Add the suffix _REG to all the register defines to better indicate
what they are.

Add a prefix to all the register bit defines to avoid namespace clashes
and to better indicate what they are.

Tidy up the whitesapce.
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>