staging: comedi: adq12b: remove 's->len_chanlist' init for analog inputs

This driver does not support async commands so the len_chanlist init is
unnecessary. Remove it and allow the core to default the value to '1'.

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>