Staging: comedi: pcl816: Correct AI scan counting

For AI commands, the scan counter should be updated after every
scan.  In DMA mode, it was being updated after every repeated
segment of the channel list.  In non-DMA mode, it was being updated
after every sample.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>