ARM: dts: omap3-gta04: Fix graph_port warning

We're currently getting a warning with make dtbs:

arch/arm/boot/dts/omap3-gta04.dtsi:720.7-727.4: Warning (graph_port):
/ocp@68000000/dss@48050000/encoder@48050c0 0/port: graph node unit
address error, expected "0"

Tested-by: H. Nikolaus Schaller <hns@goldelico.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>