[Why]
It fixes the failure to create stream for sink in the scenario
when hotplug SST and MST in sequence, and disconnect MST.

[How]
Add the fake sink back after the majority of MST rework is done.
Signed-off-by: NJerry (Fangzhi) Zuo <Jerry.Zuo@amd.com>
Reviewed-by: NNicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: NBhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Acked-by: NTony Cheng <Tony.Cheng@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>