MIPS: ingenic: jz4780: Fix I2C nodes to match DT doc

The "ingenic,jz4780-i2c" should have "ingenic,jz4770-i2c" as a fallback
compatible, as per the Device Tree documentation found in
Documentation/devicetree/bindings/i2c/ingenic,i2c.yaml.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>