iio: light: veml6030: fix IIO device retrieval from embedded device

The dev pointer that is received as an argument in the
in_illuminance_period_available_show function references the device
embedded in the IIO device, not in the i2c client.

dev_to_iio_dev() must be used to accessthe right data. The current
implementation leads to a segmentation fault on every attempt to read
the attribute because indio_dev gets a NULL assignment.

This bug has been present since the first appearance of the driver,
apparently since the last version (V6) before getting applied. A
constant attribute was used until then, and the last modifications might
have not been tested again.

Cc: stable@vger.kernel.org
Fixes: 7b779f57 ("iio: light: add driver for veml6030 ambient light sensor")
Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
Link: https://patch.msgid.link/20240913-veml6035-v1-3-0b09c0c90418@gmail.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/light/veml6030.c

@@ -99,9 +99,8 @@ static const char * const period_values[] = {
 static ssize_t in_illuminance_period_available_show(struct device *dev,
 				struct device_attribute *attr, char *buf)
 {
+	struct veml6030_data *data = iio_priv(dev_to_iio_dev(dev));
 	int ret, reg, x;
-	struct iio_dev *indio_dev = i2c_get_clientdata(to_i2c_client(dev));
-	struct veml6030_data *data = iio_priv(indio_dev);
 
 	ret = regmap_read(data->regmap, VEML6030_REG_ALS_CONF, &reg);
 	if (ret) {