The function snd_soc_unregister_card() returned 0 unconditionally and most
callers don't care to check the return value. Make it return void and
adapt the callers that didn't ignore the return value before.

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/20220621145834.198519-1-u.kleine-koenig@pengutronix.deSigned-off-by: Mark Brown <broonie@kernel.org>