ASoC: tas2764: Correct playback volume range

ASoC: tas2764: Correct playback volume range

DVC value 0xc8 is -100dB and 0xc9 is mute; this needs to map to
-100.5dB as far as the dB scale is concerned. Fix that and enable
the mute flag, so alsamixer correctly shows the control as
<0 dB .. -100 dB, mute>.

Signed-off-by: Hector Martin <marcan@marcan.st>
Fixes: ff5fd908f544 ("ASoC: tas2764: Add the driver for the TAS2764")
Signed-off-by: Martin Povišer <povik+lin@cutebit.org>
Link: https://lore.kernel.org/r/20220630075135.2221-3-povik+lin@cutebit.org
Signed-off-by: Mark Brown <broonie@kernel.org>