staging: comedi: amplc_dio200_common: use comedi_buf_write_samples()

The dev->read_subdev used in this driver for async commands returns the
full scan with each sample so it should have the SDF_PACKED subdev_flag
set.

Add the missing subdev_flags and use comedi_buf_write_samples() to add
the sample to the async buffer.

The async events will set properly by the core. A dev_warn() message will
also be output by the core if the buffer overflows. Remove the unnecessary
events and dev_err() message in the driver.

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>