iio: core: Leave private pointer NULL when no private data supplied

In iio_device_alloc() when size of the private data is 0,
the private pointer is calculated to point behind the valid data.
Leave it NULL when no private data supplied.

Fixes: 6d4ebd56 ("iio: core: wrap IIO device into an iio_dev_opaque object")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: David Lechner <dlechner@baylibre.com>
Link: https://lore.kernel.org/r/20240304140650.977784-2-andriy.shevchenko@linux.intel.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/industrialio-core.c

@@ -1654,8 +1654,10 @@ struct iio_dev *iio_device_alloc(struct device *parent, int sizeof_priv)
 		return NULL;
 
 	indio_dev = &iio_dev_opaque->indio_dev;
-	indio_dev->priv = (char *)iio_dev_opaque +
-		ALIGN(sizeof(struct iio_dev_opaque), IIO_DMA_MINALIGN);
+
+	if (sizeof_priv)
+		indio_dev->priv = (char *)iio_dev_opaque +
+			ALIGN(sizeof(*iio_dev_opaque), IIO_DMA_MINALIGN);
 
 	indio_dev->dev.parent = parent;
 	indio_dev->dev.type = &iio_device_type;