iio:trigger: Introduce iio_tigger_{set,get}_drvdata

Introduce iio_tigger_{set,get}_drvdata which allows to attach driver specific
data to a trigger. The functions wrap access to the triggers private_data field
and all current users are updated to use iio_tigger_{set,get}_drvdata instead of
directly accessing the private_data field. This is the first step towards
removing the private_data field from the iio_trigger struct.

The following coccinelle script has been used to update the drivers:
<smpl>
@@
struct iio_trigger *trigger;
expression priv;
@@
-trigger->private_data = priv
+iio_trigger_set_drv_data(trigger, priv)

@@
struct iio_trigger *trigger;
@@
-trigger->private_data
+iio_trigger_get_drv_data(trigger)
</smpl>

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/gyro/itg3200_buffer.c

@@ -81,7 +81,7 @@ void itg3200_buffer_unconfigure(struct iio_dev *indio_dev)
 static int itg3200_data_rdy_trigger_set_state(struct iio_trigger *trig,
 		bool state)
 {
-	struct iio_dev *indio_dev = trig->private_data;
+	struct iio_dev *indio_dev = iio_trigger_get_drvdata(trig);
 	int ret;
 	u8 msc;
 
@@ -129,7 +129,7 @@ int itg3200_probe_trigger(struct iio_dev *indio_dev)
 
 	st->trig->dev.parent = &st->i2c->dev;
 	st->trig->ops = &itg3200_trigger_ops;
-	st->trig->private_data = indio_dev;
+	iio_trigger_set_drvdata(st->trig, indio_dev);
 	ret = iio_trigger_register(st->trig);
 	if (ret)
 		goto error_free_irq;