UBUNTU-CVE-2026-89814: Medium severity ubuntu/linux-hwe-edge vulnerability

In the Linux kernel, the following vulnerability has been resolved: drm/amdgpu: clamp the isolation index for rings outside a partition adev->isolation[] has one slot per partition, but a ring that is not assigned to one keeps AMDGPUXCPNOPARTITION, which is ~0, so indexing the array with it is out of bounds. SDMA submissions hit this on both the isolation enforcement and the VM flush path and trip UBSAN. Fall back to the first slot the way the cleaner shader path already does, and stop taking the address before the ring type check that makes it relevant.