imx-drm: imx-hdmi: Fix DDC I2C bus property

This patch fixes the DDC I2C bus property to use the common 'ddc-i2c-bus'
property name instead of 'ddc'. This is already documented in
Documentation/devicetree/bindings/staging/imx-drm/hdmi.txt

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>