ARM: dts: lan966x: add missing uart DMA channel

The usart node of the flexcom3 block is missing the DMA channels. Add
it.
Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Tested-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20220502224127.2604333-4-michael@walle.ccSigned-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>

arch/arm/boot/dts/lan966x.dtsi

@@ -144,6 +144,9 @@ usart3: serial@200 {
 				compatible = "atmel,at91sam9260-usart";
 				reg = <0x200 0x200>;
 				interrupts = <GIC_SPI 51 IRQ_TYPE_LEVEL_HIGH>;
+				dmas = <&dma0 AT91_XDMAC_DT_PERID(9)>,
+				       <&dma0 AT91_XDMAC_DT_PERID(8)>;
+				dma-names = "tx", "rx";
 				clocks = <&nic_clk>;
 				clock-names = "usart";
 				atmel,fifo-size = <32>;