iio: hid_sensor_hub: 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/common/hid-sensors/hid-sensor-trigger.c

@@ -122,7 +122,8 @@ int hid_sensor_setup_trigger(struct iio_dev *indio_dev, const char *name,
 		dev_err(&indio_dev->dev, "Trigger Register Failed\n");
 		goto error_free_trig;
 	}
-	indio_dev->trig = attrb->trigger = trig;
+	attrb->trigger = trig;
+	indio_dev->trig = iio_trigger_get(trig);
 
 	return ret;