pinctrl: sunxi: fix nand0 function name for sun8i

In sun4/5/6/7i, all the pin function related to NAND0 controller is
named "nand0". However, in sun8i, some of the functions are named as
"nand". This patch renamed them to "nand0", for the consistency.

Signed-off-by: Icenowy Zheng <icenowy@aosc.xyz>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>