RGB666 has a pin assignment that differs from the other formats.

Fixes: fbd452ae ("pinctrl: sh-pfc: r8a77995: Add VIN4 pins, groups and function")
Signed-off-by: Ulrich Hecht <ulrich.hecht+renesas@gmail.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>