ALSA: scarlett2: Increase mixer range to +12dB

ALSA: scarlett2: Increase mixer range to +12dB

The values loaded into the mixer are 16-bit values, with 8192
representing 0dB, going up to a current maximum of 16345 (+6dB). All
supported interfaces have no problem going up to 32612 (+12dB), so
update SCARLETT2_MIXER_MAX_DB and scarlett2_mixer_values[] to allow
for this.

Tested with:
- Scarlett 2nd Gen 6i6, 18i8, 18i20
- Scarlett 3rd Gen 4i4, 8i6, 18i8, 18i20
- Scarlett 4th Gen Solo, 2i2, 4i4
- Clarett+ 2Pre, 4Pre, 8Pre
- Vocaster One and Two

Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Link: https://lore.kernel.org/r/Zj+gYT4F2XeKTD93@m.b4.vu
Signed-off-by: Takashi Iwai <tiwai@suse.de>