bugfix: Change namespace variable to nvs_namespace (C++ compatibility)

Closes https://github.com/espressif/esp-idf/pull/11028

examples/system/ulp_fsm/ulp/main/ulp_example_main.c

@@ -98,12 +98,12 @@ static void init_ulp_program(void)
 
 static void update_pulse_count(void)
 {
-    const char* namespace = "plusecnt";
+    const char* nvs_namespace = "plusecnt";
     const char* count_key = "count";
 
     ESP_ERROR_CHECK( nvs_flash_init() );
     nvs_handle_t handle;
-    ESP_ERROR_CHECK( nvs_open(namespace, NVS_READWRITE, &handle));
+    ESP_ERROR_CHECK( nvs_open(nvs_namespace, NVS_READWRITE, &handle));
     uint32_t pulse_count = 0;
     esp_err_t err = nvs_get_u32(handle, count_key, &pulse_count);
     assert(err == ESP_OK || err == ESP_ERR_NVS_NOT_FOUND);