In the Linux kernel, the following vulnerability has been resolved: drm/amd/display: Remove sink usage from DPMS [Why] stream->sink is opt

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