Fix const issues in preparation for libcxx rebase.

Change-Id: Id57474eb63334873ee5383f61eb918941dbb0984
diff --git a/init/util.cpp b/init/util.cpp
index bddc3b2..4d36dfd 100644
--- a/init/util.cpp
+++ b/init/util.cpp
@@ -355,7 +355,7 @@
 {
     int ret;
     char buf[256];
-    char *slash;
+    const char *slash;
     int width;
 
     slash = strrchr(newpath, '/');