staging: comedi: me4000: remove 'dio_nchan' boardinfo

All the boards supported by this driver have 32 digital I/O channels.
Remove the unnecessary boardinfo.

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>