iio: at91-sama5d2_adc: Use IIO_STATIC_CONST_DEVICE_ATTR()

Slightly simplify by dropping open-coded constant data iio_dev_attr
functions and using the IIO_STATIC_CONST_DEVICE_ATTR() instead.
Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Tested-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/4476a4ce852febb3eb863878e66751c787195b18.1664782676.git.mazziesaccount@gmail.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/at91-sama5d2_adc.c

@@ -2193,26 +2193,13 @@ static ssize_t at91_adc_get_watermark(struct device *dev,
 	return scnprintf(buf, PAGE_SIZE, "%d\n", st->dma_st.watermark);
 }
 
-static ssize_t hwfifo_watermark_min_show(struct device *dev,
-					 struct device_attribute *attr,
-					 char *buf)
-{
-	return sysfs_emit(buf, "%s\n", "2");
-}
-
-static ssize_t hwfifo_watermark_max_show(struct device *dev,
-					 struct device_attribute *attr,
-					 char *buf)
-{
-	return sysfs_emit(buf, "%s\n", AT91_HWFIFO_MAX_SIZE_STR);
-}
-
 static IIO_DEVICE_ATTR(hwfifo_enabled, 0444,
 		       at91_adc_get_fifo_state, NULL, 0);
 static IIO_DEVICE_ATTR(hwfifo_watermark, 0444,
 		       at91_adc_get_watermark, NULL, 0);
-static IIO_DEVICE_ATTR_RO(hwfifo_watermark_min, 0);
-static IIO_DEVICE_ATTR_RO(hwfifo_watermark_max, 0);
+
+IIO_STATIC_CONST_DEVICE_ATTR(hwfifo_watermark_min, "2");
+IIO_STATIC_CONST_DEVICE_ATTR(hwfifo_watermark_max, AT91_HWFIFO_MAX_SIZE_STR);
 
 static const struct attribute *at91_adc_fifo_attributes[] = {
 	&iio_dev_attr_hwfifo_watermark_min.dev_attr.attr,