libperfmgr: Reuse lock in NodeLooperThread

HintManager is thread-safe as it only read maps and use NodeLooperThread
to do hint and cancel.

Test: libperfmgr_test

(cherry picked from commit 8f5e70d4ccfcc17ab9e56a8d94000f0cbb43f8e0)

Change-Id: If4669dffc6c20e0bbb6861ccf59e9fe21893379d
2 files changed