__mtk_clk_simple_remove() and so also mtk_clk_simple_remove() return
zero unconditionally. Make them return no value instead and convert the
drivers making use of it to platform_driver's .remove_new().

This makes the semantics in the callers of mtk_clk_simple_remove() clearer
and prepares for the quest to make platform driver's remove function return
void. There is no semantic change.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20230430190233.878921-2-u.kleine-koenig@pengutronix.deSigned-off-by: Stephen Boyd <sboyd@kernel.org>