hwc : Fix crash during dumpsys

Dumpsys runs in different thread not in composition thread.
Accessing mdp composition frame info in dumpsys with out
synchronizing could cause crash since frame info can get reset
in composition thread.

CRs-fixed: 503268

Change-Id: If3f7d8cc9fce8b14622e666fa52583ff0cfdedd2
2 files changed