gpiolib: unify two loops initializing GPIO descriptors

We currently iterate over the descriptors owned by the GPIO device we're
adding twice with the first loop just setting the gdev pointer. It's not
used anywhere between this and the second loop so just drop the first
one and move the assignment to the second.

Reviewed-by: Kent Gibson <warthog618@gmail.com>
Link: https://lore.kernel.org/r/20241004-gpio-notify-in-kernel-events-v1-2-8ac29e1df4fe@linaro.org


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