staging: comedi: pcmuio: use comedi_buf_write_samples()

The dev->read_subdev used in this driver for async commands returns 32-bit samples
and should have the SDF_LSAMPL subdev_flag set. It also 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 COMEDI_CB_BLOCK and COMEDI_CB_EOS events will be automatically handled by the
core. Remove the unnecessary events 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>