drm/amd/display: Fix lightup regression with DP2 single display configs

[WHY]
Previous fix for multiple displays downstream of DP2 MST hub caused regression

[HOW]
Match sink IDs instead of sink struct addresses

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Charlene Liu <charlene.liu@amd.com>
Acked-by: Wayne Lin <wayne.lin@amd.com>
Signed-off-by: Michael Strauss <michael.strauss@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>