[time] Fix settimeofday() failure on ESP8266

ESP8266's settimeofday() returns EINVAL (22) directly as the return
value when the timezone parameter is non-NULL, rather than following
POSIX convention of returning -1 and setting errno. The previous
fallback code checked errno == EINVAL which never matched because
errno was never set, so the retry with nullptr never triggered.

Fix by always passing nullptr on ESP8266 since the platform requires it.

esphome/components/time/real_time_clock.cpp

@@ -88,13 +88,13 @@ void RealTimeClock::synchronize_epoch_(uint32_t epoch) {
   struct timeval timev {
     .tv_sec = static_cast<time_t>(epoch), .tv_usec = 0,
   };
+#ifdef USE_ESP8266
+  // ESP8266 settimeofday() requires tz to be nullptr
+  int ret = settimeofday(&timev, nullptr);
+#else
   struct timezone tz = {0, 0};
   int ret = settimeofday(&timev, &tz);
-  if (ret != 0 && errno == EINVAL) {
-    // Some ESP8266 frameworks abort when timezone parameter is not NULL
-    // while ESP32 expects it not to be NULL
-    ret = settimeofday(&timev, nullptr);
-  }
+#endif
 
   if (ret != 0) {
     ESP_LOGW(TAG, "setimeofday() failed with code %d", ret);