ARM: dts: clps711x: Fix serial port names

Preferred node name for serial ports is "serial".
Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Link: https://lore.kernel.org/r/20210405051658.26779-3-shc_work@mail.ru'
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

arch/arm/boot/dts/ep7209.dtsi

@@ -133,7 +133,7 @@ pwm: pwm@80000400 {
 			#pwm-cells = <1>;
 		};
 
-		uart1: uart@80000480 {
+		uart1: serial@80000480 {
 			compatible = "cirrus,ep7209-uart";
 			reg = <0x80000480 0x80>;
 			interrupts = <12 13>;
@@ -157,7 +157,7 @@ syscon2: syscon@80001100 {
 			reg = <0x80001100 0x80>;
 		};
 
-		uart2: uart@80001480 {
+		uart2: serial@80001480 {
 			compatible = "cirrus,ep7209-uart";
 			reg = <0x80001480 0x80>;
 			interrupts = <28 29>;