pinctrl: sunxi: Use pin number when calling sunxi_pmx_set

sunxi_pmx_set accepts pin number and then calculates offset by
subtracting pin_base from it. sunxi_pinctrl_gpio_get, on the other hand,
gets offset so we have to convert it to pin number so we won't get
negative value in sunxi_pmx_set.

This was only used on A10 so far, where there is only one GPIO chip with
pin_base set to 0 so it didn't matter. However H3 also requires this
workaround but have two pinmux sections, triggering problem for PL port.

Signed-off-by: Krzysztof Adamski <k@japko.eu>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>