ARM: dts: sun6i: i7: Remove useless property

The I7 DTS uses an spdif-out property with an "okay" value. However, that
property isn't documented anywhere, and isn't used anywhere either.

Remove it.
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>

arch/arm/boot/dts/sun6i-a31-i7.dts

@@ -157,7 +157,6 @@ &reg_usb1_vbus {
 &spdif {
 	pinctrl-names = "default";
 	pinctrl-0 = <&spdif_tx_pin>;
-	spdif-out = "okay";
 	status = "okay";
 };