pinctrl: sunxi: fix pin numbers passed to register offset helpers

The pin numbers passed to sunxi_*_reg helpers to get the correct
registers should be the pin offset for the PIO block, not the
absolute number we use that is based on the alphanumeric labels
Allwinner uses.

This patch subtracts .pin_base from the pin number passed to these
functions, so the driver accesses the correct registers.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Reviewed-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>