Fix addressable lights starting white at boot (#556)

Author: OttoWinter

src/esphome/light/addressable_light.cpp

@@ -128,7 +128,9 @@ void AddressableLight::write_state(LightState *state) {
   auto val = state->get_current_values();
   // don't use LightState helper, gamma correction+brightness is handled by ESPColorView
   ESPColor color = ESPColor(uint8_t(roundf(val.get_red() * 255.0f)), uint8_t(roundf(val.get_green() * 255.0f)),
-                            uint8_t(roundf(val.get_blue() * 255.0f)), uint8_t(roundf(val.get_white() * 255.0f)));
+                            uint8_t(roundf(val.get_blue() * 255.0f)),
+                            // white is not affected by brightness; so manually scale by state
+                            uint8_t(roundf(val.get_white() * val.get_state() * 255.0f)));
 
   for (int i = 0; i < this->size(); i++) {
     (*this)[i] = color;