Use comedi_buf_write_samples() to add the samples to the async buffer.
That function will handle single and multi samples writes by determining
the number of bytes to add based on the number of samples and the
bytes_per_sample().

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>