skip i2cscan after wakeup from sleep

src/main.cpp

@@ -208,7 +208,8 @@ void setup() {
   _ASSERT(loadConfig()); // includes initialize if necessary
 
   // now that we are powered, we scan i2c bus for devices
-  i2c_scan();
+  if (RTC_runmode == RUNMODE_POWERCYCLE)
+    i2c_scan();
 
 // initialize display
 #ifdef HAS_DISPLAY