iio: Add missing include guards to headers

Add include guards to the IIO headers where they are missing. This avoids
compile errors due to redefined types if a file is included more than once.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
diff --git a/include/linux/iio/trigger_consumer.h b/include/linux/iio/trigger_consumer.h
index 60d64b3..762a3d3 100644
--- a/include/linux/iio/trigger_consumer.h
+++ b/include/linux/iio/trigger_consumer.h
@@ -7,6 +7,9 @@
  * the Free Software Foundation.
  */
 
+#ifndef __LINUX_IIO_TRIGGER_CONSUMER_H__
+#define __LINUX_IIO_TRIGGER_CONSUMER_H__
+
 /**
  * struct iio_poll_func - poll function pair
  *
@@ -50,3 +53,5 @@
  */
 int iio_triggered_buffer_postenable(struct iio_dev *indio_dev);
 int iio_triggered_buffer_predisable(struct iio_dev *indio_dev);
+
+#endif