Fix a compilation warning

https_server.c

@@ -628,7 +628,9 @@ esp_err_t http_response_begin(http_context_t http_ctx, int code, const char* con
 esp_err_t http_response_write(http_context_t http_ctx, const http_buffer_t* buffer)
 {
 	size_t len;
+#if HTTPS_SERVER
 	int ret;
+#endif
 	esp_err_t err;
     if (http_ctx->state == HTTP_COLLECTING_RESPONSE_HEADERS) {
         err = http_send_response_headers(http_ctx);