only calibrate if ADC detected

src/main.cpp

@@ -408,14 +408,14 @@ void setup() {
   if (pass == startpass+1) {
     Serial.println(" done");
     delay(20);
+    Serial.print("Calibrating current sensors..");
+    set_offset();
+    Serial.println(" done");
   } else {
     Serial.println(" WARNING: ADC not detected");
     set_hex(0xF8);
     delay(500);
   }
-  Serial.print("Calibrating current sensors..");
-  set_offset();
-  Serial.println("done");
 
   Serial.print("Checking OSMC 1..");
   set_hex(0x9);