ALSA: usb-audio: Add dB range mapping for Sennheiser Communications Headset PC 8

The decibel volume range contains a negative maximum value resulting in
pipewire complaining about the device and effectivly having no sound
output. The wrong values also resulted in the headset sounding muted
already at a mixer level of about ~25%.

PipeWire BugLink: https://gitlab.freedesktop.org/pipewire/pipewire/-/issues/1049

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=212897


Signed-off-by: Timo Gurr <timo.gurr@gmail.com>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20210503110822.10222-1-tiwai@suse.de


Signed-off-by: Takashi Iwai <tiwai@suse.de>