staging: comedi: pcl818: all board types have analog inputs

All the boards supported by this driver have 16 single-ended analog input
channels. The boards can also be configued to give 8 differential inputs.

Remove the 'n_aichan_se' and 'n_aichan_diff' members from the boardinfo and
refactor pcl818_attach().

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>