iio: Mark iio_device_type as const

The iio_device_type struct is never modified, mark it as const. This allows
it to be placed in a read-only memory section, which will protect against
accidental or deliberate modification.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Link: https://lore.kernel.org/r/20211031080421.2086-1-lars@metafoo.deSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/iio_core.h

@@ -16,7 +16,7 @@ struct iio_buffer;
 struct iio_chan_spec;
 struct iio_dev;
 
-extern struct device_type iio_device_type;
+extern const struct device_type iio_device_type;
 
 struct iio_dev_buffer_pair {
 	struct iio_dev		*indio_dev;

drivers/iio/industrialio-core.c

@@ -1622,7 +1622,7 @@ static void iio_dev_release(struct device *device)
 	kfree(iio_dev_opaque);
 }
 
-struct device_type iio_device_type = {
+const struct device_type iio_device_type = {
 	.name = "iio_device",
 	.release = iio_dev_release,
 };