gralloc: Fix issue with mmap/munmap meta due to reserved size am: 5996c60385 am: e71b43ab61 am: 2b32fc3e1a am: 1b240fb2ae

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

Change-Id: If56844989afa074a23a9344eef123a4284c5aa95
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>