iio: accel: bma180: 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/accel/bma180.c

@@ -571,7 +571,7 @@ static int bma180_probe(struct i2c_client *client,
 	trig->ops = &bma180_trigger_ops;
 	iio_trigger_set_drvdata(trig, indio_dev);
 	data->trig = trig;
-	indio_dev->trig = trig;
+	indio_dev->trig = iio_trigger_get(trig);
 
 	ret = iio_trigger_register(trig);
 	if (ret)