staging: comedi: addi_apci_3120: use comedi_async 'scans_done' to detect EOA

Remove the private data member 'ai_AiActualScan' and use the comedi_async
'scans_done' member to detect the end-of-acquisition.

The function v_APCI3120_InterruptDmaMoveBlock16bit() is then just a wrapper
for comedi_buf_write_samples(). Remove it.

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>