gpio: unregister gpiochip device before removing it

commit 01cca93a9491ed95992523ff7e79dd9bfcdea8e0 upstream.

Unregister gpiochip device (used to export information through sysfs)
before removing it internally. This way removal will reverse addition.

Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>