staging: comedi: cb_pcidas: cleanup the boardinfo 4

For aesthetic reasons, rename the ai_se_chans variable to
ai_nchan. It's a bit shorter and provides the necessary
information about the variable.

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>