pinctrl: sunxi: sunxi_pconf_set: use correct offset

Some Allwinner SoCs have 2 pinctrls (PIO and R_PIO).
Previous implementation used absolute pin numbering and it was incorrect
for R_PIO pinctrl.
It's necessary to take into account the base pin number.

Fixes: 90be64e2

 ("pinctrl: sunxi: implement pin_config_set")
Signed-off-by: Andrei Lalaev <andrey.lalaev@gmail.com>
Reviewed-by: Samuel Holland <samuel@sholland.org>
Link: https://lore.kernel.org/r/20220525190423.410609-1-andrey.lalaev@gmail.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>