The function imx_icc_unregister() 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/20220718121409.171773-9-u.kleine-koenig@pengutronix.deSigned-off-by: Georgi Djakov <djakov@kernel.org>