ARM: shmobile: koelsch: Remove non-existent i2c6 pinmux

On r8a7791, i2c6 (aka iic3) doesn't need pinmux, but the koelsch dts
refers to non-existent pinmux configuration data:

pinmux core: sh-pfc does not support function i2c6
sh-pfc e6060000.pfc: invalid function i2c6 in map table

Remove it to fix this.

Fixes: commit 1d41f36a ("ARM: shmobile:
       koelsch dts: Add VDD MPU regulator for DVFS")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Olof Johansson <olof@lixom.net>

arch/arm/boot/dts/r8a7791-koelsch.dts

@@ -275,11 +275,6 @@ msiof0_pins: spi1 {
 		renesas,function = "msiof0";
 	};
 
-	i2c6_pins: i2c6 {
-		renesas,groups = "i2c6";
-		renesas,function = "i2c6";
-	};
-
 	usb0_pins: usb0 {
 		renesas,groups = "usb0";
 		renesas,function = "usb0";
@@ -420,8 +415,6 @@ eeprom@50 {
 };
 
 &i2c6 {
-	pinctrl-names = "default";
-	pinctrl-0 = <&i2c6_pins>;
 	status = "okay";
 	clock-frequency = <100000>;