iio:light:ltr501 Fix timestamp alignment issue.

One of a class of bugs pointed out by Lars in a recent review.
iio_push_to_buffers_with_timestamp assumes the buffer used is aligned
to the size of the timestamp (8 bytes).  This is not guaranteed in
this driver which uses an array of smaller elements on the stack.
Here we use a structure on the stack.  The driver already did an
explicit memset so no data leak was possible.

Forced alignment of ts is not strictly necessary but probably makes
the code slightly less fragile.

Note there has been some rework in this driver of the years, so no
way this will apply cleanly all the way back.

Fixes: 2690be90 ("iio: Add Lite-On ltr501 ambient light / proximity sensor driver")
Reported-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: <Stable@vger.kernel.org>

drivers/iio/light/ltr501.c

@@ -1243,13 +1243,16 @@ static irqreturn_t ltr501_trigger_handler(int irq, void *p)
 	struct iio_poll_func *pf = p;
 	struct iio_dev *indio_dev = pf->indio_dev;
 	struct ltr501_data *data = iio_priv(indio_dev);
-	u16 buf[8];
+	struct {
+		u16 channels[3];
+		s64 ts __aligned(8);
+	} scan;
 	__le16 als_buf[2];
 	u8 mask = 0;
 	int j = 0;
 	int ret, psdata;
 
-	memset(buf, 0, sizeof(buf));
+	memset(&scan, 0, sizeof(scan));
 
 	/* figure out which data needs to be ready */
 	if (test_bit(0, indio_dev->active_scan_mask) ||
@@ -1268,9 +1271,9 @@ static irqreturn_t ltr501_trigger_handler(int irq, void *p)
 		if (ret < 0)
 			return ret;
 		if (test_bit(0, indio_dev->active_scan_mask))
-			buf[j++] = le16_to_cpu(als_buf[1]);
+			scan.channels[j++] = le16_to_cpu(als_buf[1]);
 		if (test_bit(1, indio_dev->active_scan_mask))
-			buf[j++] = le16_to_cpu(als_buf[0]);
+			scan.channels[j++] = le16_to_cpu(als_buf[0]);
 	}
 
 	if (mask & LTR501_STATUS_PS_RDY) {
@@ -1278,10 +1281,10 @@ static irqreturn_t ltr501_trigger_handler(int irq, void *p)
 				       &psdata, 2);
 		if (ret < 0)
 			goto done;
-		buf[j++] = psdata & LTR501_PS_DATA_MASK;
+		scan.channels[j++] = psdata & LTR501_PS_DATA_MASK;
 	}
 
-	iio_push_to_buffers_with_timestamp(indio_dev, buf,
+	iio_push_to_buffers_with_timestamp(indio_dev, &scan,
 					   iio_get_time_ns(indio_dev));
 
 done: