copybit: Fix type conversion error for GCC 4.7

    GCC 4.7 has stricter type conversion rules in copybit.cpp

Change-Id: I7f8572e2d9416ccb2ba17e707c7f75a2e69d69cf
Merge branch 'cm-11.0' of https://github.com/CyanogenMod/android_hardware_qcom_display-caf into cm-11.0