[bsp] fix incompatible type for finsh_system_init in bsp/lpc824

bsp/lpc824/applications/startup.c

@@ -27,7 +27,7 @@
 
 extern int  rt_application_init(void);
 #ifdef RT_USING_FINSH
-extern void finsh_system_init(void);
+extern int finsh_system_init(void);
 extern void finsh_set_device(const char* device);
 #endif