arm64: dts: marvell: armada-37xx: add UART clock

Add the missing clock property to armada-3700 UART node.

This clock will be used to derive the prescaler value to comply with
the requested baudrate.
Signed-off-by: Miquel Raynal <miquel.raynal@free-electrons.com>
Acked-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>

arch/arm64/boot/dts/marvell/armada-37xx.dtsi

@@ -135,6 +135,7 @@ i2c1: i2c@11080 {
 			uart0: serial@12000 {
 				compatible = "marvell,armada-3700-uart";
 				reg = <0x12000 0x200>;
+				clocks = <&xtalclk>;
 				interrupts = <GIC_SPI 11 IRQ_TYPE_LEVEL_HIGH>;
 				status = "disabled";
 			};