gpio: cdev: fix missed label sanitizing in debounce_setup()

When adding sanitization of the label, the path through
edge_detector_setup() that leads to debounce_setup() was overlooked.
A request taking this path does not allocate a new label and the
request label is freed twice when the request is released, resulting
in memory corruption.

Add label sanitization to debounce_setup().

Cc: stable@vger.kernel.org
Fixes: b3449087

 ("gpio: cdev: sanitize the label before requesting the interrupt")
Signed-off-by: Kent Gibson <warthog618@gmail.com>
[Bartosz: rebased on top of the fix for empty GPIO labels]
Co-developed-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>