staging: comedi: adl_pci9118: remove 'int_ai_func' from private data

The devpriv->usedma flag can be checked to determine which handler
function should be used to transfer the analog input data. Do that
instead and remove the member from the private data.

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>