CS420x codecs seem to deal only the single amps of ADC nodes even
though the nodes receive multiple inputs.  This leads to the
inconsistent amp value after S3/S4 resume, for example.

The fix is just to set codec->single_adc_amp flag.  Then the driver
handles these ADC amps as if single connections.
Reported-and-tested-by: Vasil Zlatanov <vasil.zlatanov@gmail.com>
Cc: <stable@vger.kernel.org> # 3.9+
Signed-off-by: Takashi Iwai <tiwai@suse.de>