Make macro defined event base variables immutable and update license

components/esp_event/include/esp_event_base.h

@@ -1,16 +1,8 @@
-// Copyright 2018 Espressif Systems (Shanghai) PTE LTD
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//         http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
+/*
+ * SPDX-FileCopyrightText: 2018-2023 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
 
 #ifndef ESP_EVENT_BASE_H_
 #define ESP_EVENT_BASE_H_
@@ -20,8 +12,8 @@ extern "C" {
 #endif
 
 // Defines for declaring and defining event base
-#define ESP_EVENT_DECLARE_BASE(id) extern esp_event_base_t id
-#define ESP_EVENT_DEFINE_BASE(id) esp_event_base_t id = #id
+#define ESP_EVENT_DECLARE_BASE(id) extern esp_event_base_t const id
+#define ESP_EVENT_DEFINE_BASE(id) esp_event_base_t const id = #id
 
 // Event loop library types
 typedef const char*  esp_event_base_t; /**< unique pointer to a subsystem that exposes events */