iio: adc: mxs-lradc: 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.
Add a comment on why the buffer is the size it is as not immediately
obvious.

Found during an audit of all calls of this function.

Fixes: 6dd112b9f8 ("iio: adc: mxs-lradc: Add support for ADC driver")
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Andreas Klinger <ak@it-klinger.de>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20210613152301.571002-4-jic23@kernel.org

drivers/iio/adc/mxs-lradc-adc.c

@@ -115,7 +115,8 @@ struct mxs_lradc_adc {
 	struct device		*dev;
 
 	void __iomem		*base;
-	u32			buffer[10];
+	/* Maximum of 8 channels + 8 byte ts */
+	u32			buffer[10] __aligned(8);
 	struct iio_trigger	*trig;
 	struct completion	completion;
 	spinlock_t		lock;