CVE-2026-98997: drm/amdgpu/userq: only accept doorbell BOs as queue doorbell

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

drm/amdgpu/userq: only accept doorbell BOs as queue doorbell

amdgpuuserqgetdoorbellindex() pins any BO passed as doorbellhandle into the doorbell domain. For a regular BO, TTM moves it with ttmbomovenull() and its contents are lost. Since an importer on the same device gets the exporter's GEM object, a client can do this to a buffer another client shared with it.

Reject BOs that were not created in the doorbell domain.

v2: drop the error message, use a local abo variable (Christian)

(cherry picked from commit f7497bbc19db4821c62b9d97b31c9086feb2d917)