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

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

Change-Id: I514aa5f8d9b51cd9f2a742c2b40c8c94e136f1fa
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>