iio: adc: stm32: fix null pointer on defer_probe error

dev_err_probe() calls __device_set_deferred_probe_reason()
on -EPROBE_DEFER error. If device pointer to driver core
private structure is not initialized, an null pointer error occurs.
This pointer is set on iio_device_register() call for iio device.

dev_err_probe() must be called with the device which is probing.
Replace iio device by its parent device.

Fixes: 0e346b2cfa ("iio: adc: stm32-adc: add vrefint calibration support")
Signed-off-by: Olivier Moysan <olivier.moysan@foss.st.com>
Reviewed-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Link: https://lore.kernel.org/r/20211122143809.2332-1-olivier.moysan@foss.st.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/stm32-adc.c

@@ -1987,7 +1987,7 @@ static int stm32_adc_populate_int_ch(struct iio_dev *indio_dev, const char *ch_n
 			/* Get calibration data for vrefint channel */
 			ret = nvmem_cell_read_u16(&indio_dev->dev, "vrefint", &vrefint);
 			if (ret && ret != -ENOENT) {
-				return dev_err_probe(&indio_dev->dev, ret,
+				return dev_err_probe(indio_dev->dev.parent, ret,
 						     "nvmem access error\n");
 			}
 			if (ret == -ENOENT)