pinctrl: sh-pfc: r8a7795: Use PINMUX_SINGLE() for I2C

Now we have PINMUX_SINGLE(). Let's use it instead of PINMUX_IPSR_NOGP()

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>