On unknown/unhandled ioctls the driver should return an error, so
userspace knows it tried to use something unsupported.

Cc: stable@vger.kernel.org
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>
Reviewed-by: NAlex Williamson <alex.williamson@redhat.com>
Signed-off-by: NZhenyu Wang <zhenyuw@linux.intel.com>