hwc: Silence some logging

Summary: kills some log spam, silences errors caused on every screen
refresh when display/vsync cannot keep up with 60fps.

Thanks to @jrior001 for initially submitting the patch, and dealing with
me being stubborn about DEBUG.

Test Plan: confirmed

Reviewers: anders3408, randall.rushing, jriordan001, synergy

Reviewed By: synergy

Differential Revision: http://review.codefirex.com/D52