std.cfg: Added more <valid>-tags.

Author: orbitcowboy

cfg/std.cfg

@@ -1323,6 +1323,7 @@
     <leak-ignore/>
     <arg nr="1">
       <not-uninit/>
+      <valid>0:255</valid>
     </arg>
   </function>
   <!-- int mbsinit(const mbstate_t* ps); -->