staging: comedi: pcl812: remove unnecessary s->len_chanlist init

The subdevice 'len_chanlist' member is only used with async command
support. Remove the initialization of this member for the subdevices
that do not support commands. The core will then correctly initialize
it to the default value of '1'.

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>