Defer calling begin() on digital buses

NeoPixelBus requires that all parallel I2S bus members be constructed
before any of them call Begin().  Implement this by deferring the
call to the end of bus construction.

Fixes #4301.

wled00/bus_manager.cpp

@@ -410,7 +410,7 @@ std::vector<LEDType> BusDigital::getLEDTypes() {
   };
 }
 
-void BusDigital::reinit() {
+void BusDigital::begin() {
   if (!_valid) return;
   PolyBus::begin(_busPtr, _iType, _pins);
 }
@@ -910,7 +910,7 @@ void BusManager::on() {
       if (busses[i]->isDigital() && busses[i]->getPins(pins)) {
         if (pins[0] == LED_BUILTIN || pins[1] == LED_BUILTIN) {
           BusDigital *bus = static_cast<BusDigital*>(busses[i]);
-          bus->reinit();
+          bus->begin();
           break;
         }
       }