libcopybit: Add missing return statement

Change-Id: I662699b7418eba2c4792ed6c7c7b628762ebe03b
(cherry picked from commit f2e940109252c63b6e21f929e45ba794dfe12b95)
Merge branch 'cm-11.0' of github.com:CyanogenMod/android_hardware_qcom_display-caf into HEAD