pinctrl: renesas: rzg2l: Move arg and index in the main function block

Move arg and index in the main block of the function as they are used by
more than one case block of switch-case (3 out of 4 for arg, 2 out of 4
for index). In this way some lines of code are removed.

Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20231207070700.4156557-4-claudiu.beznea.uj@bp.renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>