pinctrl: core: Make pins const unsigned int pointer in struct group_desc

It's unclear why it's not a const unsigned int pointer from day 1.
Make the pins member const unsigned int pointer in struct group_desc.
Update necessary APIs.

Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20231204160033.1872569-3-andriy.shevchenko@linux.intel.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>