staging: comedi: amplc_pci224: use comedi_async 'scans_done' to detect EOA

staging: comedi: amplc_pci224: use comedi_async 'scans_done' to detect EOA

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

Use the helper function comedi_nscans_left() to determine the number of scans
available in the async buffer or left in the command.

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>