drm/amd/amdgpu: Update update_config() logic

[Why]
For MST case: when update_config is called to disable a stream,
this clears the settings for all the streams on that link.
We should only clear the settings for the stream that was disabled.

[How]
Clear the settings after the call to remove display is called.

Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Leo (Hanghong) Ma <hanghong.ma@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>