iio: adc: max11100: Constify struct iio_chan_spec

max11100_channels is not modified and can therefore be made const to
allow the compiler to put it in read-only memory.

Before:
   text    data     bss     dec     hex filename
   3776    1168       0    4944    1350 drivers/iio/adc/max11100.o

After:
   text    data     bss     dec     hex filename
   3968     976       0    4944    1350 drivers/iio/adc/max11100.o
Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/max11100.c

@@ -37,7 +37,7 @@ struct max11100_state {
 	u8 buffer[3] ____cacheline_aligned;
 };
 
-static struct iio_chan_spec max11100_channels[] = {
+static const struct iio_chan_spec max11100_channels[] = {
 	{ /* [0] */
 		.type = IIO_VOLTAGE,
 		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |