Initialise ADC in main, not in sensor drivers

platform/cc2538dk/contiki-main.c

@@ -43,6 +43,7 @@
  */
 /*---------------------------------------------------------------------------*/
 #include "contiki.h"
+#include "dev/adc.h"
 #include "dev/leds.h"
 #include "dev/sys-ctrl.h"
 #include "dev/scb.h"
@@ -208,6 +209,8 @@ main(void)
   process_start(&tcpip_process, NULL);
 #endif /* NETSTACK_CONF_WITH_IPV6 */
 
+  adc_init();
+
   process_start(&sensors_process, NULL);
 
   energest_init();

platform/cc2538dk/dev/als-sensor.c

@@ -79,7 +79,6 @@ configure(int type, int value)
     GPIO_SET_INPUT(GPIO_A_BASE, ADC_ALS_OUT_PIN_MASK);
     ioc_set_over(GPIO_A_NUM, ADC_ALS_OUT_PIN, IOC_OVERRIDE_ANA);
 
-    adc_init();
     break;
   }
   return 0;