staging: comedi: pcl711: tidy up pcl711_ai_insn()

For aesthetic reasons, rename this function to help with greps.

Tidy up the function a bit to follow the comedi driver norm.

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>