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: If1afb1533344e994398b9b6f5bd3dfb125313416
Merge "Fix crash on boot" into cm-11.0
Merge branch 'cm-11.0' of https://github.com/CyanogenMod/android_hardware_samsung into temp