staging: comedi: comedi_buf: introduce comedi_buf_write_samples()

Introduce a generic method to write samples to the async buffer.

The number of samples is first checked against the number of samples that
would fill the async buffer. The size of each sample is determined using
the bytes_per_sample() helper. If all the samples will fit in the async
buffer they are written to the buffer using comedi_write_array_to_buffer().

This will allow converting all the comedi drivers to use a common method to
write data to the async buffer.

Since comedi_write_array_to_buffer() sets the COMEDI_CB_BLOCK event after
writing the data, those events can be removed from the drivers.

In addition, comedi_inc_scan_progress() will automatically detect the end of
scan and set the COMEDI_CB_EOS event. Those events can also be removed from
the drivers.

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>