ARM: at91/dt: at91sam9g20: switch ssc compatible string

As the SSC integrate in at91sam9g20 support frame sync length
extension, so switch compatible string to support this feature.
Signed-off-by: Bo Shen <voice.shen@atmel.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>

arch/arm/boot/dts/at91sam9g20.dtsi

@@ -22,6 +22,10 @@ i2c0: i2c@fffac000 {
 				compatible = "atmel,at91sam9g20-i2c";
 			};
 
+			ssc0: ssc@fffbc000 {
+				compatible = "atmel,at91sam9rl-ssc";
+			};
+
 			adc0: adc@fffe0000 {
 				atmel,adc-startup-time = <40>;
 			};