libhwc2.1: don't construct string if debug log is disabled am: afbc2293eb am: 55aba26701

Original change: https://googleplex-android-review.googlesource.com/c/platform/hardware/google/graphics/zuma/+/24581795

Change-Id: Idfc9c282005100d70e2f5bfb5cf4fe6463ef8b0d
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>