CVE-2023-54098 drm/i915/gvt: fix gvt debugfs destroy

In the Linux kernel, the following vulnerability has been resolved: drm/i915/gvt: fix gvt debugfs destroy When gvt debug fs is destroyed, need to have a sane check if drm minor's debugfs root is still available or not, otherwise in case like device remove through unbinding, drm minor's debugfs...