gpio: sysfs: use cleanup guards for the sysfs_lock mutex

Shrink the code and remove some goto labels by using guards around the
sysfs_lock mutex.

Reviewed-by: Kent Gibson <warthog618@gmail.com>
Link: https://lore.kernel.org/r/20241031-gpio-notify-sysfs-v4-2-142021c2195c@linaro.org


Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>