ARM: dts: imx6dl-prtvt7: Remove unused 'sound-dai-cells' from ssi1 node

The 'fsl,ssi' documentation doesn't say anything about specifying this.
Signed-off-by: Robin van der Gracht <robin@protonic.nl>
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx6dl-prtvt7.dts

@@ -290,7 +290,6 @@ &snvs_pwrkey {
 };
 
 &ssi1 {
-	#sound-dai-cells = <0>;
 	status = "okay";
 };