drm/amd/display: Fix bug where refresh rate becomes fixed

This issue occurs if refresh rate range is very small and lfc is not used.
When frame spikes occur, refresh rate becomes fixed and will not restore properly

Signed-off-by: Anthony Koo <Anthony.Koo@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>