Copter: update notify during ESC calibration

The notify devices including the RGB were not being updated meaning the main LED was normally frozen or off during calibration.  The desired behaviour is that it flashes red, blue, yellow.

ArduCopter/esc_calibration.cpp

@@ -93,10 +93,16 @@ void Copter::esc_calibration_passthrough()
     // arm motors
     motors->armed(true);
     motors->enable();
-    
+
+    uint32_t last_notify_update_ms = 0;
     while(1) {
         // flash LEDS
         AP_Notify::flags.esc_calibration = true;
+        uint32_t now = AP_HAL::millis();
+        if (now - last_notify_update_ms > 20) {
+            last_notify_update_ms = now;
+            update_notify();
+        }
 
         // read pilot input
         read_radio();