CVE-2026-63884 drm/i915: Fix potential UAF in TTM object purge

In the Linux kernel, the following vulnerability has been resolved: drm/i915: Fix potential UAF in TTM object purge TLDR: The bo-ttm object might be changed by calling ttmbovalidate, move casting it to an i915tt object later to actually get the right pointer. A user reported hitting the following...