CVE-2026-31540 drm/i915/gt: Check set_default_submission() before deferencing

In the Linux kernel, the following vulnerability has been resolved: drm/i915/gt: Check setdefaultsubmission before deferencing When the i915 driver firmware binaries are not present, the setdefaultsubmission pointer is not set. This pointer is dereferenced during suspend anyways. Add a check to...