Fix crash on boot

There is a race condition where the sysfs-vsync thread accesses a value
(in particular a function ptr) that may not have been set yet as this
is done externally.

Change-Id: Ica01616af59f171c255c9bc99db4857eb8f32817
Merge pull request #3 from CyanogenMod/cm-11.0

Fix crash on boot