When unknown source is detected for sampling clock, corresponding label was not added for node on procfs. This commit adds it. Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp> Link: https://lore.kernel.org/r/20191030080644.1704-3-o-takashi@sakamocchi.jp Signed-off-by: Takashi Iwai <tiwai@suse.de>