ASoC: codecs: wcd938x: fix dB range for HPHL and HPHR

[ Upstream commit c03226ba ]

dB range for HPHL and HPHR gains are from +6dB to -30dB in steps of
1.5dB with register values range from 0 to 24.

Current code maps these dB ranges incorrectly, fix them to allow proper
volume setting.

Fixes: e8ba1e05

 ("ASoC: codecs: wcd938x: add basic controls")
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20230705125723.40464-1-srinivas.kandagatla@linaro.org
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>