gpiolib: Fix scope-based gpio_device refcounting

Commit 9e4555d1 ("gpiolib: add support for scope-based management to
gpio_device") sought to add scope-based gpio_device refcounting, but
erroneously forgot a negation of IS_ERR_OR_NULL().

As a result, gpio_device_put() is not called if the gpio_device pointer
is valid (meaning the ref is leaked), but only called if the pointer is
NULL or an ERR_PTR().

While at it drop a superfluous trailing semicolon.

Fixes: 9e4555d1 ("gpiolib: add support for scope-based management to gpio_device")
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>