gpio: remove remaining users of gpiochip_remove() retval

Some drivers accidentally still use the return value from
gpiochip_remove(). Get rid of them so we can simplify this function
and get rid of the return value.

Cc: Abdoulaye Berthe <berthe.ab@gmail.com>
Acked-by: Alexandre Courbot <acourbot@nvidia.com>
Acked-by: Javier Martinez Canillas <javier@dowhile0.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>