iio:adc:ad799x: Make chan_spec const in ad799x_chip_config struct

Signed-off-by: NPeter Meerwald <pmeerw@pmeerw.net>
Acked-by: NLars-Peter Clausen <lars@metafoo.de>
Signed-off-by: NJonathan Cameron <jic23@kernel.org>

drivers/iio/adc/ad799x.c

@@ -107,7 +107,7 @@ enum {
  * @info:		pointer to iio_info struct
  */
 struct ad799x_chip_config {
-	struct iio_chan_spec		channel[9];
+	const struct iio_chan_spec	channel[9];
 	u16				default_config;
 	const struct iio_info		*info;
 };