gpio: pca953x: Make platform teardown callback return void

All platforms that provide a teardown callback return 0. New users are
supposed to not make use of platform support, so there is no
functionality lost.

This patch is a preparation for making i2c remove callbacks return void.

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Bartosz Golaszewski <brgl@bgdev.pl>
Signed-off-by: Wolfram Sang <wsa@kernel.org>