staging: comedi: das_08: remove the 8254 'channels' usage

The internal 8254 'channels' count is the same as the comedi
subdevice 'n_chan'. There is no need to keep the internal
count.

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>