gpio: sysfs: fix memory leak in gpiod_sysfs_set_active_low

commit 49d2ca84 upstream.

Fix memory leak in the gpio sysfs interface due to failure to drop
reference to device returned by class_find_device when setting the
gpio-line polarity.

Fixes: 07697461 ("gpiolib: add support for changing value polarity
in sysfs")
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
[ luis: backported to 3.16:
  - file rename: drivers/gpio/gpiolib-sysfs.c -> drivers/gpio/gpiolib.c ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

drivers/gpio/gpiolib.c

@@ -960,6 +960,7 @@ int gpiod_sysfs_set_active_low(struct gpio_desc *desc, int value)
 
 	status = sysfs_set_active_low(desc, dev, value);
 
+	put_device(dev);
 unlock:
 	mutex_unlock(&sysfs_lock);