adc: Make driver config_info structure const.

Change-Id: Ide974b66da3b785c676f5bbd4f3f5f248797c4e5
Signed-off-by: Marcus Shawcroft <marcus.shawcroft@arm.com>
diff --git a/drivers/adc/adc_ti_adc108s102.c b/drivers/adc/adc_ti_adc108s102.c
index f50d11b..506bb5f 100644
--- a/drivers/adc/adc_ti_adc108s102.c
+++ b/drivers/adc/adc_ti_adc108s102.c
@@ -228,7 +228,7 @@
 
 struct ti_adc108s102_data adc108s102_data;
 
-static struct ti_adc108s102_config adc108s102_config = {
+static const struct ti_adc108s102_config adc108s102_config = {
 	.spi_port = CONFIG_ADC_TI_ADC108S102_SPI_PORT_NAME,
 	.spi_config_flags = CONFIG_ADC_TI_ADC108S102_SPI_CONFIGURATION,
 	.spi_freq = CONFIG_ADC_TI_ADC108S102_SPI_MAX_FREQ,