i3c: Make i3c_master_unregister() return void

The function returned zero unconditionally. Switch the return type to void
and simplify the callers accordingly.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/r/20230318233311.265186-2-u.kleine-koenig@pengutronix.de


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>