iio: adc: at91_adc: use of_device_get_match_data() helper

This is a small tidy-up. The of_device_get_match_data() helper retrieves
the driver data from the OF table, without needed to explicitly know the
table variable (since it can retrieve it from the driver object).
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Reviewed-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20200930135048.11530-2-alexandru.ardelean@analog.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/at91_adc.c

@@ -829,8 +829,6 @@ static u32 calc_startup_ticks_9x5(u32 startup_time, u32 adc_clk_khz)
 	return ticks;
 }
 
-static const struct of_device_id at91_adc_dt_ids[];
-
 static int at91_adc_probe_dt_ts(struct device_node *node,
 	struct at91_adc_state *st, struct device *dev)
 {
@@ -878,8 +876,7 @@ static int at91_adc_probe_dt(struct iio_dev *idev,
 	if (!node)
 		return -EINVAL;
 
-	st->caps = (struct at91_adc_caps *)
-		of_match_device(at91_adc_dt_ids, &pdev->dev)->data;
+	st->caps = (struct at91_adc_caps *)of_device_get_match_data(&pdev->dev);
 
 	st->use_external = of_property_read_bool(node, "atmel,adc-use-external-triggers");