pinctrl: sunxi: Fix A64 UART mux value

To use pin PF4 as the RX signal of UART0, we have to write 0b011 into
the respective pin controller register.
Fix the wrong value we had in our table so far.

Fixes: 96851d39 ("drivers: pinctrl: add driver for Allwinner A64 SoC")
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>