staging: comedi: das16m1: use comedi_buf_write_samples()

Use comedi_buf_write_samples() to add the samples to the async buffer.
The number of bytes to add is determined automatically 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>