ASoC: codecs: wcd938x: fix return value of mixer put function

wcd938x_ear_pa_put_gain, wcd938x_set_swr_port and  wcd938x_set_compander
currently returns zero eventhough it changes the value.
Fix this, so that change notifications are sent correctly.

e8ba1e05 ("ASoC: codecs: wcd938x: add basic controls")
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>