iio: st-sensors: add support for single full scale device

Some sensors could have only one full scale value. This means that the
sensor hasn't a full scale register. This commit add a check on the
configured full scale address to support such kind of sensors.

Signed-off-by: Giuseppe Barba <giuseppe.barba@st.com>
Acked-by: Denis Ciocca <denis.ciocca@st.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/common/st_sensors/st_sensors_core.c

@@ -126,6 +126,9 @@ static int st_sensors_set_fullscale(struct iio_dev *indio_dev, unsigned int fs)
 	int err, i = 0;
 	struct st_sensor_data *sdata = iio_priv(indio_dev);
 
+	if (sdata->sensor_settings->fs.addr == 0)
+		return 0;
+
 	err = st_sensors_match_fs(sdata->sensor_settings, fs, &i);
 	if (err < 0)
 		goto st_accel_set_fullscale_error;