libhwc2.1: Fix incorrect DRM_FORMAT for RGBA_FP16 am: 3ec426448d

Original change: https://googleplex-android-review.googlesource.com/c/platform/hardware/google/graphics/common/+/25650513

Change-Id: I83fcc5c89f70422888b4e67c9aa15fc3c27a269c
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>