[Why] For MST, link not disabled until all streams disabled [How] Add check for stream_count before setting link_active = false for MST Signed-off-by: Anthony Koo <Anthony.Koo@amd.com> Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com> Acked-by: Leo Li <sunpeng.li@amd.com> Signed-off-by: Alex Deucher <alexander.deucher@amd.com>