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: Idb39331dd0be66bb5ec5f5861c8c834a67458aa5
Signed-off-by: Automerger Merge Worker <[email protected]>