gralloc: fix find_last_rect()

Change-Id: Ib9346bac87c4264f610afde442a8ea8231922aae
Merge branch 'cm-12.0' of https://github.com/archidroid/android_hardware_samsung_slsi_exynos4 into cm-12.0

Conflicts:
	libgralloc_ump/gralloc_module.cpp