drm_hwcomposer: Remove hardcoded PAGE_SIZE usage in gralloc_helper am: b9ae59025f

Original change: https://android-review.googlesource.com/c/platform/external/drm_hwcomposer/+/3017877

Change-Id: I9061f31fcf8c180a772a42a85ea468794c2d3cb5
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>