清除unused编译警告 (#21)

* 清除unused编译警告

portevent_m.c文件52行，'result' 定义未使用
编译提示: warning: unused variable 'result'

port/portevent_m.c

@@ -49,7 +49,7 @@ BOOL
 xMBMasterPortEventGet( eMBMasterEventType * eEvent )
 {
     rt_uint32_t recvedEvent;
-    BOOL result;
+
     /* waiting forever OS event */
     rt_event_recv(&xMasterOsEvent,
             EV_MASTER_READY | EV_MASTER_FRAME_RECEIVED | EV_MASTER_EXECUTE |