ASoC: rt711-sdca: add the notification when volume changed

This patch adds the return value when the volume settings were changed.
The userspace application might monitor the kcontrols to check which control changed.

Signed-off-by: Shuming Fan <shumingf@realtek.com>
Link: https://lore.kernel.org/r/20210422103235.22048-1-shumingf@realtek.com
Signed-off-by: Mark Brown <broonie@kernel.org>