staging: comedi: pcl711: fix software trigger for board->is_8112

The acl-8112 boards also need to write a value to the software
trigger register in order to start an A/D conversion. Remove the
if (!board->is_8112) test so that the write is always done.

Also, the analog input mode does not need to be set each time for
multiple samples. Move the pcl711_ai_set_mode() out of the for loop.

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>