drm/amd/display: Fix DP MST timeslot issue when fallback happened

[Why]
When USB4 DP link training failed and fell back to lower link rate,
the time slot calculation uses the verified_link_cap.
And the verified_link_cap was not updated to the new one.
It caused the wrong VC payload time-slot was allocated.

[How]
Updated verified_link_cap with the new one from cur_link_settings
after the LT completes successfully.

Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Wayne Lin <wayne.lin@amd.com>
Signed-off-by: Cruise Hung <Cruise.Hung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>