Enable Clippy and fix warnings am: ed58226b5a

Original change: https://android-review.googlesource.com/c/trusty/app/secretkeeper/+/3106019

Change-Id: Ifedd3a6595073c854d225a296b36531fbd64b2b5
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>