drm/amd/powerplay: improve OD code robustness

add protection code to avoid lower frequency trigger over drive.

Reviewed-by: Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Tianci Yin <tianci.yin@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>