iio: iio.h: fix a warning at the kernel-doc markup

There's a warning at iio.h kernel-doc markup:

	./include/linux/iio/iio.h:644: WARNING: Unknown target name: "devm".

Because it is using {devm_}foo notation. Well, this is not
a valid kernel-doc notation. Also, it prevents creating hyperlinks
to other documentation functions.

So, replace it to a better notation.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/d8f2275c438c459ede4e6fba03ce719cc6ad898b.1599660067.git.mchehab+huawei@kernel.orgSigned-off-by: Jonathan Corbet <corbet@lwn.net>

include/linux/iio/iio.h

@@ -641,7 +641,7 @@ static inline struct iio_dev *iio_device_get(struct iio_dev *indio_dev)
  *
  * This utility must be called between IIO device allocation
  * (via devm_iio_device_alloc()) & IIO device registration
- * (via {devm_}iio_device_register()).
+ * (via iio_device_register() and devm_iio_device_register())).
  * By default, the device allocation will also assign a parent device to
  * the IIO device object. In cases where devm_iio_device_alloc() is used,
  * sometimes the parent device must be different than the device used to