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 directory has already been removed, then intel_gvt_debugfs_clean() would act upon dangling pointer like below oops. i915 0000:00:02.0: Direct firmware load for i915/gvt/vid_0x8086_did_0x1926_rid_0x0a.golden_hw_state failed with error -2 i915 0000:00:02.0: MDEV: Registered Console: switching to colour dummy device 80x25 i915 0000:00:02.0: MDEV: Unregi