arm64: dts: hisilicon: Align UART nodename with dtschema

Fix dtschema validator warnings like:
    uart@f8015000: $nodename:0: 'uart@f8015000' does not match '^serial(@[0-9a-f,]+)*$'
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Wei Xu <xuwei5@hisilicon.com>

arch/arm64/boot/dts/hisilicon/hi6220.dtsi

@@ -302,7 +302,7 @@ stub_clock: stub_clock {
 			mboxes = <&mailbox 1 0 11>;
 		};
 
-		uart0: uart@f8015000 {	/* console */
+		uart0: serial@f8015000 {	/* console */
 			compatible = "arm,pl011", "arm,primecell";
 			reg = <0x0 0xf8015000 0x0 0x1000>;
 			interrupts = <GIC_SPI 36 IRQ_TYPE_LEVEL_HIGH>;
@@ -311,7 +311,7 @@ uart0: uart@f8015000 {	/* console */
 			clock-names = "uartclk", "apb_pclk";
 		};
 
-		uart1: uart@f7111000 {
+		uart1: serial@f7111000 {
 			compatible = "arm,pl011", "arm,primecell";
 			reg = <0x0 0xf7111000 0x0 0x1000>;
 			interrupts = <GIC_SPI 37 IRQ_TYPE_LEVEL_HIGH>;
@@ -325,7 +325,7 @@ uart1: uart@f7111000 {
 			status = "disabled";
 		};
 
-		uart2: uart@f7112000 {
+		uart2: serial@f7112000 {
 			compatible = "arm,pl011", "arm,primecell";
 			reg = <0x0 0xf7112000 0x0 0x1000>;
 			interrupts = <GIC_SPI 38 IRQ_TYPE_LEVEL_HIGH>;
@@ -337,7 +337,7 @@ uart2: uart@f7112000 {
 			status = "disabled";
 		};
 
-		uart3: uart@f7113000 {
+		uart3: serial@f7113000 {
 			compatible = "arm,pl011", "arm,primecell";
 			reg = <0x0 0xf7113000 0x0 0x1000>;
 			interrupts = <GIC_SPI 39 IRQ_TYPE_LEVEL_HIGH>;
@@ -349,7 +349,7 @@ uart3: uart@f7113000 {
 			status = "disabled";
 		};
 
-		uart4: uart@f7114000 {
+		uart4: serial@f7114000 {
 			compatible = "arm,pl011", "arm,primecell";
 			reg = <0x0 0xf7114000 0x0 0x1000>;
 			interrupts = <GIC_SPI 40 IRQ_TYPE_LEVEL_HIGH>;