ASoC: simple-card-utils: Make asoc_simple_clean_reference() return void

asoc_simple_clean_reference() returns zero unconditionally. Letting it
return void instead makes it easier to see in the caller that there is no
error to handle.

This is a preparation for making platform remove callbacks return void.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20220605153537.26591-1-u.kleine-koenig@pengutronix.de


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