ALSA: usb-audio - Add "cval->res = 384" quirk for Logitech Webcam C600

One more affected devices: Logitech Webcam C600 (046d:0808)

Volume range before quirk is 6400, after (also real) is 16.

Signed-off-by: Alexey Fisher <bug-track@fisher-privat.net>
Signed-off-by: Takashi Iwai <tiwai@suse.de>