ALSA: hda/cs8409: Fix Full Scale Volume setting for all variants

All current variants (Bullseye/Warlock/Cyborg) should be using
reduced volume (-6dB) for better speaker protection.

Refactor to make more explicit the meaning and setting of
Full Scale Volume setting to avoid future confusion.

Signed-off-by: Stefan Binding <sbinding@opensource.cirrus.com>
Signed-off-by: Vitaly Rodionov <vitalyr@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20220328115614.15761-4-vitalyr@opensource.cirrus.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>