staging: comedi: pcl818: absorb pcl818_ai_mode13dma_int()

Absorb this function into pcl818_ai_cmd_mode() and simplify the code.

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>