pinctrl: sunxi: a64: Rename function csi0 to csi

The A64 only has one CSI (camera sensor interface) controller. The
datasheet also lists the function as CSI_XXX instead of CSI0_XXX.

Rename the function names now before any there are any users.

Fixes: 96851d39 ("drivers: pinctrl: add driver for Allwinner A64 SoC")
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>