pinctrl: sh-pfc: r8a7796: Correct VIN4 18-bit pins

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

Fixes: 8db6cbab ("pinctrl: sh-pfc: r8a7796: Add VIN4, VIN5 pins, groups and functions")
Signed-off-by: Ulrich Hecht <ulrich.hecht+renesas@gmail.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>