!102 修正对用户态关闭fd 3时的系统调用实现

Merge pull request !102 from jesven/fix_close_fd3

components/lwp/lwp_syscall.c

@@ -473,7 +473,7 @@ int sys_open(const char *name, int flag, ...)
 /* syscall: "close" ret: "int" args: "int" */
 int sys_close(int fd)
 {
-    if ((0 <= fd) && (fd <= 2))
+    if ((0 <= fd) && (fd <= DFS_FD_OFFSET))
     {
         return 0;
     }