iio: at91-sama5d2: Use dev_to_iio_dev() in sysfs callbacks

Using `dev_get_drvdata()` in IIO sysfs callbacks to get a pointer to the
IIO device is a relic from the very early days of IIO. The IIO core as well
as most other drivers have switched over to using `dev_to_iio_dev()`
instead.

This driver is one of the last few drivers remaining that uses the outdated
idiom, update it. This will allow to eventually update the IIO core to no
longer set the drvdata for the IIO device and free it up for driver usage.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Link: https://lore.kernel.org/r/20211019082929.30503-2-lars@metafoo.de
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
(cherry picked from commit 0d376dc)

Author: larsclausen

drivers/iio/adc/at91-sama5d2_adc.c

@@ -1825,7 +1825,7 @@ static void at91_adc_hw_init(struct iio_dev *indio_dev)
 static ssize_t at91_adc_get_fifo_state(struct device *dev,
 				       struct device_attribute *attr, char *buf)
 {
-	struct iio_dev *indio_dev = dev_get_drvdata(dev);
+	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
 	struct at91_adc_state *st = iio_priv(indio_dev);
 
 	return scnprintf(buf, PAGE_SIZE, "%d\n", !!st->dma_st.dma_chan);
@@ -1834,7 +1834,7 @@ static ssize_t at91_adc_get_fifo_state(struct device *dev,
 static ssize_t at91_adc_get_watermark(struct device *dev,
 				      struct device_attribute *attr, char *buf)
 {
-	struct iio_dev *indio_dev = dev_get_drvdata(dev);
+	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
 	struct at91_adc_state *st = iio_priv(indio_dev);
 
 	return scnprintf(buf, PAGE_SIZE, "%d\n", st->dma_st.watermark);