tfp410_fini() always returns zero. Make it return no value which makes it
easier to see in the callers that there is no error to handle.

Also the return value of i2c and platform driver remove callbacks is
ignored anyway. This prepares making i2c and platform remove callbacks
return void, too.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220428162803.185275-1-u.kleine-koenig@pengutronix.de