Added missing ADC start command, fixed return value / error behavior of ADC init

ROMFS/scripts/rc.sensors

@@ -8,6 +8,7 @@
 #
 
 ms5611 start
+adc start
 
 if mpu6000 start
 then

apps/sensors/sensors.cpp

@@ -640,8 +640,8 @@ Sensors::adc_init()
 
 	_fd_adc = open("/dev/adc0", O_RDONLY | O_NONBLOCK);
 	if (_fd_adc < 0) {
-		warn("/dev/adc0");
+		warnx("/dev/adc0");
-		errx(1, "FATAL: no ADC found");
+		warnx(1, "FATAL: no ADC found");
 	}
 }