ARM: dts: sun9i: Fix I2C bus warnings

dtc has new checks for I2C buses. The sun9i-a80 dts file has a node named
'i2c' which causes a false positive warning. As the node is a RSB bus,
correct the node name to be 'rsb' to fix the warnings.

arch/arm/boot/dts/sun9i-a80-cubieboard4.dtb: Warning (i2c_bus_reg): /soc/i2c@8003400/codec@e89:reg: I2C address must be less than 10-bits, got "0xe89"
arch/arm/boot/dts/sun9i-a80-cubieboard4.dtb: Warning (i2c_bus_reg): /soc/i2c@8003400/pmic@745:reg: I2C address must be less than 10-bits, got "0x745"
arch/arm/boot/dts/sun9i-a80-optimus.dtb: Warning (i2c_bus_reg): /soc/i2c@8003400/codec@e89:reg: I2C address must be less than 10-bits, got "0xe89"
arch/arm/boot/dts/sun9i-a80-optimus.dtb: Warning (i2c_bus_reg): /soc/i2c@8003400/pmic@745:reg: I2C address must be less than 10-bits, got "0x745"

Cc: Maxime Ripard <maxime.ripard@bootlin.com>
Cc: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>