iio: accel: bma180: Fix buffer alignment in iio_push_to_buffers_with_timestamp()

To make code more readable, use a structure to express the channel
layout and ensure the timestamp is 8 byte aligned.

Found during an audit of all calls of this function.

Fixes: b9a6a237 ("iio:bma180: Drop _update_scan_mode()")
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Peter Meerwald <pmeerw@pmeerw.net>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20210501170121.512209-2-jic23@kernel.org

drivers/iio/accel/bma180.c

@@ -162,7 +162,11 @@ struct bma180_data {
 	int scale;
 	int bw;
 	bool pmode;
-	u8 buff[16]; /* 3x 16-bit + 8-bit + padding + timestamp */
+	/* Ensure timestamp is naturally aligned */
+	struct {
+		s16 chan[4];
+		s64 timestamp __aligned(8);
+	} scan;
 };
 
 enum bma180_chan {
@@ -938,12 +942,12 @@ static irqreturn_t bma180_trigger_handler(int irq, void *p)
 			mutex_unlock(&data->mutex);
 			goto err;
 		}
-		((s16 *)data->buff)[i++] = ret;
+		data->scan.chan[i++] = ret;
 	}
 
 	mutex_unlock(&data->mutex);
 
-	iio_push_to_buffers_with_timestamp(indio_dev, data->buff, time_ns);
+	iio_push_to_buffers_with_timestamp(indio_dev, &data->scan, time_ns);
 err:
 	iio_trigger_notify_done(indio_dev->trig);