CVE-2026-98926: drm/amd/display: Remove sink usage from DPMS

In the Linux kernel, the following vulnerability has been resolved:

drm/amd/display: Remove sink usage from DPMS

[Why] stream->sink is optional and can be null, so should always be checked before dereference. Additionally, most of its usage in DPMS sequences is for stream->sink->link, which can be replaced with stream->link, as the two should always be the same.

[How] Replace stream->sink->link in DPMS on/off Add assert to USB4 BW allocation where sink is required Avoid inconsistencies in resource access, e.g. don't repeat stream->link after it was already saved to a local variable Pull out effective VPG calculation to helper getter Formatting fixes