gpiolib: make value setters have return values

Change the in-kernel consumer interface for GPIOs: make all variants of
value setters that don't have a return value, return a signed integer
instead. That will allow these routines to indicate failures to callers.

This doesn't change the implementation just yet, we'll do it in
subsequent commits.

We need to update the gpio-latch module as it passes the address of
value setters as a function pointer argument and thus cares about its
type.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Link: https://lore.kernel.org/r/20250220-gpio-set-retval-v2-2-bc4cfd38dae3@linaro.org


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