ALSA: hda - Mute unused capture sources for Realtek codecs

When a Realtek codec has a matrix-style capture-source selection, we
need to scan all connections instead of only imux items.  Otherwise some
input might be kept unmuted.  Although the corresponding input must be
dead so there should be no input from it, it's still safer to mute the
route completely.

Signed-off-by: Takashi Iwai <tiwai@suse.de>