pinctrl: at91: Remove pioc_index from struct at91_gpio_chip

The pioc_idx member of struct at91_gpio_chip is write only, just remove it.

Reviewed-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20230216-gpio-at91-immutable-v2-2-326ef362dbc7@kernel.org


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