staging: comedi: pcmmio: remove unused members in private data

The 'pol' and 'enab' members in the private data are never used. The
'num' member is set during the attach but never used. Remove 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>