Add missing <functional> include am: 5b5fe9ef2d am: 0eafc4a437

Original change: https://android-review.googlesource.com/c/platform/external/libldac/+/2759541

Change-Id: Ifecccad7a804047d0e75f7e171b0b11cb44e7619
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>