pinctrl: sunxi: fix a typo when merging A20 support to A10 driver

When merging A20 pinctrl support to A10 pinctrl driver, the I2C function
of PI3 is wrongly written as "i2c3" (it should be "i2c4").

Fix this typo.

Fixes: cad4e209 ("pinctrl: sunxi: add support of R40 to A10 pinctrl driver")
Reported-by: Mark Kettenis <mark.kettenis@xs4all.nl>
Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>