ASoC: tlv320adcx140: Fix digital gain range

According to its datasheet, the digital gain should be -100 dB when
CHx_DVOL is 1 and 27 dB when CHx_DVOL is 255. But with the current
dig_vol_tlv, "Digital CHx Out Volume" shows 27.5 dB if CHx_DVOL is 255
and -95.5 dB if CHx_DVOL is 1. This commit fixes this bug.

Fixes: 689c7655

 ("ASoC: tlv320adcx140: Add the tlv320adcx140 codec driver family")
Signed-off-by: Camel Guo <camelg@axis.com>
Link: https://lore.kernel.org/r/20200908090417.16695-1-camel.guo@axis.com
Signed-off-by: Mark Brown <broonie@kernel.org>