iio: dac: ad5686: Constify static struct iio_chan_spec

These are never modified and can be made const to allow the compiler to
put it in read-only memory.

Before:
   text    data     bss     dec     hex filename
   6642   12608      64   19314    4b72 drivers/iio/dac/ad5686.o

After:
   text    data     bss     dec     hex filename
  16946    2304      64   19314    4b72 drivers/iio/dac/ad5686.o
Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Acked-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/dac/ad5686.c

@@ -206,12 +206,12 @@ static const struct iio_chan_spec_ext_info ad5686_ext_info[] = {
 }
 
 #define DECLARE_AD5693_CHANNELS(name, bits, _shift)		\
-static struct iio_chan_spec name[] = {				\
+static const struct iio_chan_spec name[] = {			\
 		AD5868_CHANNEL(0, 0, bits, _shift),		\
 }
 
 #define DECLARE_AD5686_CHANNELS(name, bits, _shift)		\
-static struct iio_chan_spec name[] = {				\
+static const struct iio_chan_spec name[] = {			\
 		AD5868_CHANNEL(0, 1, bits, _shift),		\
 		AD5868_CHANNEL(1, 2, bits, _shift),		\
 		AD5868_CHANNEL(2, 4, bits, _shift),		\
@@ -219,7 +219,7 @@ static struct iio_chan_spec name[] = {				\
 }
 
 #define DECLARE_AD5676_CHANNELS(name, bits, _shift)		\
-static struct iio_chan_spec name[] = {				\
+static const struct iio_chan_spec name[] = {			\
 		AD5868_CHANNEL(0, 0, bits, _shift),		\
 		AD5868_CHANNEL(1, 1, bits, _shift),		\
 		AD5868_CHANNEL(2, 2, bits, _shift),		\
@@ -231,7 +231,7 @@ static struct iio_chan_spec name[] = {				\
 }
 
 #define DECLARE_AD5679_CHANNELS(name, bits, _shift)		\
-static struct iio_chan_spec name[] = {				\
+static const struct iio_chan_spec name[] = {			\
 		AD5868_CHANNEL(0, 0, bits, _shift),		\
 		AD5868_CHANNEL(1, 1, bits, _shift),		\
 		AD5868_CHANNEL(2, 2, bits, _shift),		\

drivers/iio/dac/ad5686.h

@@ -104,7 +104,7 @@ typedef int (*ad5686_read_func)(struct ad5686_state *st, u8 addr);
 struct ad5686_chip_info {
 	u16				int_vref_mv;
 	unsigned int			num_channels;
-	struct iio_chan_spec		*channels;
+	const struct iio_chan_spec	*channels;
 	enum ad5686_regmap_type		regmap_type;
 };