Rewrite nid_vol/mute assignment for clearity, and check line connection
before adding control for it.
Signed-off-by: NLydia Wang <lydiawang@viatech.com.cn>
Signed-off-by: NLogan Li <loganli@viatech.com.cn>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>