gralloc: Fix issue with mmap/munmap meta due to reserved size am: 5996c60385 am: 8947bd6917 am: dd0f8850cc am: afe3405b42

Original change: https://googleplex-android-review.googlesource.com/c/platform/hardware/qcom/sm7250/display/+/19355798

Change-Id: I6872c839a2de426303a98c555844e6a52279b6c8
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>