gpio: sysfs: emit chardev line-state events on GPIO export

We already emit a CONFIG_RELEASED event when a line is unexported over
sysfs (this is handled by gpiod_free()) but we don't do the opposite
when it's exported. This adds the missing call to
gpiod_line_state_notify().

Reviewed-by: Kent Gibson <warthog618@gmail.com>
Link: https://lore.kernel.org/r/20241031-gpio-notify-sysfs-v4-3-142021c2195c@linaro.org


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