staging: comedi: dt3000: rename the interrupt flag defines

For aesthetics, rename these defines so they have association
with the register. Move them closer to the register define and
use the BIT macro to define them.

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>