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

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: 7b779f573c48 ("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.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>