drm/amd/display: AVMUTE simplification

[Why]
Simplify AVMUTE logic in coding

[How]
Avoid multiple calls on TMDS AVMUTE
as updated logic now demands it.

Signed-off-by: Chris Park <Chris.Park@amd.com>
Reviewed-by: Charlene Liu <Charlene.Liu@amd.com>
Acked-by: Qingqing Zhuo <Qingqing.Zhuo@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>