gpiolib: of: Use local variables

Instead of modifying the contents of the array of values read
in from a phandle, use local variables to store the values.
This makes the code easier to read and the array immutable.

Reviewed-by: Alex Elder <elder@riscstar.com>
Tested-by: Yixun Lan <dlan@gentoo.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20250225-gpio-ranges-fourcell-v3-1-860382ba4713@linaro.org


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