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: I0f0e878750c16571e9140a23f582341c338e74cc
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>