staging: comedi: das_08: remove the unneeded 8254 variables and defines

Now that the driver is using the 8253 helper functions, remove the
unused variables in the i8254_struct as well as the unused defines
for the 8254 register offsets.

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