The remove callback is only called after probe completed successfully.
In this case platform_set_drvdata() was called with a non-NULL argument
and so chip is never NULL.

Also note that returning an error code from a remove callback doesn't
result in the device staying bound. It's still removed and devm
callbacks are called.

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>