gpio: twl4030: Don't return an error after WARN in .remove

gpio: twl4030: Don't return an error after WARN in .remove

Returning a non-zero value in a platform driver's remove callback only
results in an error message ("remove callback returned a non-zero value.
This will be ignored.", see platform_remove()), and then the device is
removed anyhow.

As there was just a WARN_ON triggered, return 0 to drop the follow up
warning. The latter output is hardly relevant after the big WARN splat.

This is a preparation for making platform remove callbacks return void.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>