iio: Add dev_to_iio_dev() helper function

This patch adds a helper function for retriving a iio_dev struct from a device
struct. Currently we open-code this in two different ways. One is using
dev_get_drvdata on the device and the other is using container_of. The new
helper function uses the container_of solution as it creates slightly smaller
code and also will eventually free up the drvdata pointer for usage by invidual
drivers.

Signed-off-by: Lars-Peter Clausen <[e-mail]>
Acked-by: Jonathan Cameron <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

include/linux/iio/iio.h

···
 		put_device(&indio_dev->dev);
 };
 
+/**
+ * dev_to_iio_dev() - Get IIO device struct from a device struct
+ * @dev: The device embedded in the IIO device
+ *
+ * Note: The device must be a IIO device, otherwise the result is undefined.
+ */
+static inline struct iio_dev *dev_to_iio_dev(struct device *dev)
+{
+	return container_of(dev, struct iio_dev, dev);
+}
+
 /* Can we make this smaller? */
 #define IIO_ALIGN L1_CACHE_BYTES
 /**