docs: iio: fix example formatting

This line is part of the code snippet, so it has to be nested in order
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Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Link: https://lore.kernel.org/r/20210215143511.25471-2-luca@lucaceresoli.netSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/iio/iio_configfs.rst

@@ -71,7 +71,7 @@ kernel module following the interface in include/linux/iio/sw_trigger.h::
 	.ops = &iio_trig_sample_ops,
   };
 
-module_iio_sw_trigger_driver(iio_trig_sample);
+  module_iio_sw_trigger_driver(iio_trig_sample);
 
 Each trigger type has its own directory under /config/iio/triggers. Loading
 iio-trig-sample module will create 'trig-sample' trigger type directory