drm/xe/guc_submit: add back fix

Daniele noticed that the fix in commit 2d2be279 ("drm/xe: fix UAF
around queue destruction") looks to have been unintentionally removed as
part of handling a conflict in some past merge commit. Add it back.

Fixes: ac44ff7c ("Merge tag 'drm-xe-fixes-2024-10-10' of https://gitlab.freedesktop.org/drm/xe/kernel

 into drm-fixes")
Reported-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: <stable@vger.kernel.org> # v6.12+
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://lore.kernel.org/r/20250603174213.1543579-2-matthew.auld@intel.com