ARM: dts: imx6qdl-sabreauto: Pass the DDC I2C bus

On imx6qdl-sabreauto the HDMI DDC bus is connected to I2C2, so
pass the 'ddc-i2c-bus' property accordingly.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>