Documentation: omap-twl4030: Move ti,codec property to optional

ti,codec property is not used in omap-twl4030 driver in linux kernel but
we keep it as optional property, so that the existing dtbs do not
become noncompliant after the change on other OS.
Signed-off-by: Marek Belisko <marek@goldelico.com>
Acked-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

Documentation/devicetree/bindings/sound/omap-twl4030.txt

@@ -4,9 +4,9 @@ Required properties:
 - compatible: "ti,omap-twl4030"
 - ti,model: Name of the sound card (for example "omap3beagle")
 - ti,mcbsp: phandle for the McBSP node
-- ti,codec: phandle for the twl4030 audio node
 
 Optional properties:
+- ti,codec: phandle for the twl4030 audio node
 - ti,mcbsp-voice: phandle for the McBSP node connected to the voice port of twl
 - ti, jack-det-gpio: Jack detect GPIO
 - ti,audio-routing: List of connections between audio components.
@@ -59,5 +59,4 @@ sound {
 	ti,model = "omap3beagle";
 
 	ti,mcbsp = <&mcbsp2>;
-	ti,codec = <&twl_audio>;
 };