pinctrl: renesas: rzg2l: Replace of_node_to_fwnode() with more suitable API

pinctrl: renesas: rzg2l: Replace of_node_to_fwnode() with more suitable API

of_node_to_fwnode() is a IRQ domain specific implementation of
of_fwnode_handle(). Replace the former with more suitable API.

Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Tested-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/20240822230104.707812-1-andy.shevchenko@gmail.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>