staging:iio: Add support for multiple buffers

Route all buffer writes through the demux.
Addition or removal of a buffer results in tear down and
setup of all the buffers for a given device.

Signed-off-by: Jonathan Cameron <jic23@kernel.org>
Tested-by: srinivas pandruvada <srinivas.pandruvada@intel.com>

drivers/iio/adc/ad7476.c

@@ -76,7 +76,7 @@ static irqreturn_t ad7476_trigger_handler(int irq, void  *p)
 	if (indio_dev->scan_timestamp)
 		((s64 *)st->data)[1] = time_ns;
 
-	iio_push_to_buffer(indio_dev->buffer, st->data);
+	iio_push_to_buffers(indio_dev, st->data);
 done:
 	iio_trigger_notify_done(indio_dev->trig);