ALSA: usb-audio: fix CM6206 register definitions

fix typo after a recent commit causing headphones to have no sound

Fixes: ad43d528

 (ALSA: usb-audio: Define registers for CM6206)
Signed-off-by: Amadeusz Sławiński <amade@asmblr.net>
Signed-off-by: Takashi Iwai <tiwai@suse.de>