staging: comedi: das1800: use comedi_buf_write_samples()

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().

Also, remove the unnecessary COMEDI_CB_BLOCK event. comedi_buf_write_samples()
will automatically add that event after adding the samples to the async
buffer.

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>