ARM: OMAP: dss-common: fix Panda's DVI DDC channel

Panda's DVI connector's DDC pins are connected to OMAP's third i2c bus.
With non-DT, the bus number was 3, and that is what is used in the
dss-common.c which contains the platform data for Panda's DVI.

However, with DT, the bus number is 2. As we now only have DT boot for
Panda, we have to change the bus number to make DVI EDID read
operational.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>