BugLink: https://bugs.launchpad.net/bugs/538895

The OR has verified that both position_fix=1 and model=6stack-dig are
necessary to have capture function properly. (The existing 3stack-6ch
model quirk seems to be incorrect.)
Reported-by: NReuben Bailey <reuben.e.bailey@gmail.com>
Tested-by: NReuben Bailey <reuben.e.bailey@gmail.com>
Cc: <stable@kernel.org>
Signed-off-by: NDaniel T Chen <crimsun@ubuntu.com>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>