ALSA: hda - fix a typo by changing mute_led_nid to cap_mute_led_nid

BugLink: https://bugs.launchpad.net/bugs/1329580


Cc: David Henningsson <david.henningsson@canonical.com>
Cc: Kailang Yang <kailang@realtek.com>
Signed-off-by: Hui Wang <hui.wang@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>