drm/amd/display: Clear FAMS flag if FAMS doesn't reduce vlevel

[Description]
- If we find that applying FAMS doesn't reduce the voltage level,
  we will not use it
- Ensure to clear the stream flags indicating FAMS if we hit this
  case

Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Alvin Lee <Alvin.Lee2@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>