ARM: dts: rockchip: remove rockchip,bus-index from rk3xxx i2c0

This is a remnant from the first i2c driver iteration that seems to have
been forgotten and thus made its way into the dtsi. Remove it.
Signed-off-by: NHeiko Stuebner <heiko@sntech.de>

arch/arm/boot/dts/rk3xxx.dtsi

@@ -135,7 +135,6 @@
 		#size-cells = <0>;
 
 		rockchip,grf = <&grf>;
-		rockchip,bus-index = <0>;
 
 		clock-names = "i2c";
 		clocks = <&cru PCLK_I2C0>;