staging: comedi: pcl816: remove 'ai_ns_min' from boardinfo

This member of the boardinfo is the same for all board types. Remove this
data from the 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>