Do not unnecessarily re-inflate camera preview

Camera preview inflation was happening every time the keyguard
visibility changed, causing jank and making sysui drop frames.

Ultimately, the symptom was AOD flashing after pressing power.

Fixes: 130878131
Test: press power to go from and to AOD
Test: double tap power to launch camera (preview is still available)
Test: press power to lock device from launcher
Change-Id: Id3df83d59dcd123a71b37297e9ab70a1e8a52c90