pinctrl: UniPhier: PH1-Pro5: add I2C ch6 pin-mux setting

The initial version of this driver missed to add I2C ch6 pin-muxing.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>