[bsp][lpc824] fixed error: incomplete type is not allowed

bsp/lpc824/rtconfig.h

@@ -80,7 +80,7 @@
 // </c>
 // <c1>Using Mutex
 //  <i>Using Mutex
-//#define RT_USING_MUTEX
+#define RT_USING_MUTEX
 // </c>
 // <c1>Using Event
 //  <i>Using Event