Fix "hide su" patch for 3.10

Without this, "ls system/xbin" returns "ls: system/xbin/su: No such file or directory"
if root is disabled in Developer Settings.
This happens because EXT4 uses "readdir" instead of "iterate".
3.18 kernel, instead, unconditionally goes for the "iterate" way here
and that explains why I'm not seeing this error there.

Change-Id: I26426683df0fd199a80f053294f352e31754bec5