iio: prox: as3935: 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 uses of
iio_push_to_buffers_with_timestamp()

Fixes: 37b1ba2c ("iio: proximity: as3935: fix buffer stack trashing")
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Matt Ranostay <matt.ranostay@konsulko.com>
Acked-by: Matt Ranostay <matt.ranostay@konsulko.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20210501170121.512209-15-jic23@kernel.org

drivers/iio/proximity/as3935.c

@@ -59,7 +59,11 @@ struct as3935_state {
 	unsigned long noise_tripped;
 	u32 tune_cap;
 	u32 nflwdth_reg;
-	u8 buffer[16]; /* 8-bit data + 56-bit padding + 64-bit timestamp */
+	/* Ensure timestamp is naturally aligned */
+	struct {
+		u8 chan;
+		s64 timestamp __aligned(8);
+	} scan;
 	u8 buf[2] ____cacheline_aligned;
 };
 
@@ -225,8 +229,8 @@ static irqreturn_t as3935_trigger_handler(int irq, void *private)
 	if (ret)
 		goto err_read;
 
-	st->buffer[0] = val & AS3935_DATA_MASK;
-	iio_push_to_buffers_with_timestamp(indio_dev, &st->buffer,
+	st->scan.chan = val & AS3935_DATA_MASK;
+	iio_push_to_buffers_with_timestamp(indio_dev, &st->scan,
 					   iio_get_time_ns(indio_dev));
 err_read:
 	iio_trigger_notify_done(indio_dev->trig);