It seems that AD1986A cannot manage the dynamic pin on/off for
auto-muting, but rather gets confused.  Since each output has own amp,
let's use it instead.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=64971
Cc: <stable@vger.kernel.org> [v3.11+]
Signed-off-by: Takashi Iwai <tiwai@suse.de>