ALSA: hda/ca0132 - Fix recording from mode id 0x8

Incorrect ADC is picked in ca0132_capture_pcm_prepare(),
where it assumes multiple streams while there is one stream
per ADC. Note that ca0132_capture_pcm_cleanup() already does
the right thing.

The Chromebook Pixel has a microphone under the keyboard that
is attached to node id 0x8. Before this fix, recording would
always go to the main internal mic (node id 0x7).

Signed-off-by: Hsin-Yu Chao <hychao@chromium.org>
Reviewed-by: Dylan Reid <dgreid@chromium.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>