ARM: dts: vf610-twr: remove useless property for sound card.

This was added by:
Commit 8128c4f3 ("ARM: dts: vf610-twr: Add simple-card support.")

This useless property may cause some confusions for users.
Signed-off-by: Xiubo Li <Li.Xiubo@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>

arch/arm/boot/dts/vf610-twr.dts

@@ -76,7 +76,6 @@ sound {
 
 		simple-audio-card,cpu {
 			sound-dai = <&sai2>;
-			master-clkdir-out;
 			frame-master;
 			bitclock-master;
 		};