ASoC: codecs: wcd934x: Set digital gain range correctly

digital gain range is -84dB min to 40dB max, however this was not
correctly specified in the range.

Fix this by with correct range!

Fixes: 1cde8b82 ("ASoC: wcd934x: add basic controls")
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>