drm/xe: Check return value of GGTT workqueue allocation

drm/xe: Check return value of GGTT workqueue allocation

Workqueue allocation can fail, so check the return value of the GGTT
workqueue allocation and fail driver initialization if the allocation
fails.

Fixes: dd08ebf6c352 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
Cc: stable@vger.kernel.org
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://lore.kernel.org/r/20251022005538.828980-2-matthew.brost@intel.com
(cherry picked from commit 1f1314e8e71385bae319e43082b798c11f6648bc)
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>