The function idma64_remove() returns zero unconditionally. Make it
return void.

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/20221014161250.468687-1-u.kleine-koenig@pengutronix.deSigned-off-by: Vinod Koul <vkoul@kernel.org>