Use comedi_buf_write_samples() to add the sample to the async buffer.

The async events COMEDI_CB_BLOCK and COMEDI_CB_EOS will be detected and set
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>