gpio: sysfs: fix memory leak in gpiod_export_link

commit 0f303db08df0df9bd0966443ad6001e63960af16 upstream.

Fix memory leak in the gpio sysfs interface due to failure to drop
reference to device returned by class_find_device when creating a link.

Fixes: a4177ee7 ("gpiolib: allow exported GPIO nodes to be named using sysfs links")
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>