android_keymaster.cpp: Fix compiler warning am: 536357d615

Original change: https://android-review.googlesource.com/c/platform/system/keymaster/+/3097437

Change-Id: Ia613e08133bf95474302e3d7b9ac97c9c4ff149d
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>