ASoC: max9768: Fix event generation for playback mute

The max9768 has a custom control for playback mute which unconditionally
returns 0 from the put() operation, rather than returning 1 on change to
ensure notifications are generated to userspace. Check to see if the value
has changed and return appropriately.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://patch.msgid.link/20241112-asoc-max9768-event-v1-1-ba5d50599787@kernel.org


Signed-off-by: Mark Brown <broonie@kernel.org>