iio: gyro: itg3200: Fix indio_dev->trig assignment

This can result in wrong reference count for trigger device, call
iio_trigger_get to increment reference.
Refer to http://www.spinics.net/lists/linux-iio/msg13669.html for discussion
with Jonathan.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
Cc: Stable@vger.kernel.org

drivers/iio/gyro/itg3200_buffer.c

@@ -132,7 +132,7 @@ int itg3200_probe_trigger(struct iio_dev *indio_dev)
 		goto error_free_irq;
 
 	/* select default trigger */
-	indio_dev->trig = st->trig;
+	indio_dev->trig = iio_trigger_get(st->trig);
 
 	return 0;