ALSA: virtuoso: Xonar DS: fix polarity of front output

The two DACs for the front output and the surround/center/LFE/back
outputs are wired up out of phase, so when channels are duplicated,
their sound can cancel out each other and result in a weaker bass
response.  To fix this, reverse the polarity of the neutron flow to
the front output.

Reported-any-tested-by: Daniel Hill <daniel@enemyplanet.geek.nz>
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Cc: 2.6.34+ <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>