pinctrl: renesas: Mark local variable with const in ->set_mux()

We are not going to change pins in the ->set_mux() callback. Mark
the local variable with a const qualifier. While at it, make it
also unsigned.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20231204160033.1872569-2-andriy.shevchenko@linux.intel.com


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