gpio: wm831x: don't print out global GPIO numbers in debugfs callbacks

gpio: wm831x: don't print out global GPIO numbers in debugfs callbacks

In order to further limit the number of references to the GPIO base
number stored in struct gpio_chip, replace the global GPIO numbers in
the output of debugfs callbacks by hardware offsets.

Reviewed-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20250826-gpio-dbg-show-base-v1-3-7f27cd7f2256@linaro.org
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>