gralloc: Fix issue with mmap/munmap meta due to reserved size am: c9a0d7b113

Original change: https://googleplex-android-review.googlesource.com/c/platform/hardware/qcom/sm8150/display/+/19355927

Change-Id: Iccb2cf86bfae931985c82095da9742323cf9bd7c
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>