libc: fix typo in waitid() declaration.

The implementation file uses the correct spelling.

Change-Id: I572e336f8695a9754267c8d2e0a67b1b69bacb06
diff --git a/libc/include/sys/wait.h b/libc/include/sys/wait.h
index 573e220..b30b7ec 100644
--- a/libc/include/sys/wait.h
+++ b/libc/include/sys/wait.h
@@ -56,7 +56,7 @@
  */
 typedef int idtype_t;
 
-extern int  waidit(idtype_t which, id_t id, siginfo_t *info, int options);
+extern int  waitid(idtype_t which, id_t id, siginfo_t *info, int options);
 
 __END_DECLS