staging: iio: core: Avoid NULL pointer de-ref in case indio_dev->setup_ops are not in use

Drivers may not need setup_ops at all, so let the core supply
some empty ops.

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Acked-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/iio/industrialio-core.c

@@ -854,6 +854,8 @@ static const struct file_operations iio_buffer_fileops = {
 	.compat_ioctl = iio_ioctl,
 };
 
+static const struct iio_buffer_setup_ops noop_ring_setup_ops;
+
 int iio_device_register(struct iio_dev *indio_dev)
 {
 	int ret;
@@ -882,6 +884,10 @@ int iio_device_register(struct iio_dev *indio_dev)
 	if (indio_dev->modes & INDIO_BUFFER_TRIGGERED)
 		iio_device_register_trigger_consumer(indio_dev);
 
+	if ((indio_dev->modes & INDIO_ALL_BUFFER_MODES) &&
+		indio_dev->setup_ops == NULL)
+		indio_dev->setup_ops = &noop_ring_setup_ops;
+
 	ret = device_add(&indio_dev->dev);
 	if (ret < 0)
 		goto error_unreg_eventset;