staging: comedi: pcl812: remove 'ai_data_len' from private data

This member of the private data is only used in the initial dma setup.
Refactor that code to not need it and remove the member.

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>

diff --cc drivers/staging/comedi/drivers/pcl812.c
Simple merge