Fix error in safety ADC

stm-firmware/include/reflow-controller/safety-adc.h

@@ -37,6 +37,7 @@ enum safety_adc_check_result {
 				SAFETY_ADC_CHECK_VREF_HIGH = (1U<<1),
 				SAFETY_ADC_CHECK_TEMP_LOW = (1U<<2),
 				SAFETY_ADC_CHECK_TEMP_HIGH = (1U<<3),
+				SAFETY_ADC_INTERNAL_ERROR = (1U<<4),
 				};
 
 void safety_adc_init();

stm-firmware/safety-adc.c

@@ -132,7 +132,7 @@ enum safety_adc_check_result handle_safety_adc()
 			break;
 		default:
 			safety_meas_channel = SAFETY_ADC_MEAS_VREF;
-			return -2000;
+			return SAFETY_ADC_INTERNAL_ERROR;
 		}
 	}