staging: comedi: pcl711: remove unnecessary test of 'board->is_8112'

At the end of an asynchronous command, the analog input is returned
to software triggered mode. For the non-8112 style boards the mode
PCL711_MODE_DEFAULT and PCL711_MODE_SOFTTRIG are identical. Just set
the mode to PCL711_MODE_SOFTTRIG and remove the test.

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>