arm64: dts: ti: k3-am642-hummingboard-t: correct rs485 rts polarity

The RS485 transceiver RE (Receiver enable) and DE (Driver enable) are
shorted and connected to both RTS/CTS of the SoC UART.
RE is active-low, DE is active-high.

Remove the "rs485-rts-active-low" flag to match RTS polarity with DE,
and fix communication in both transmit and receive directions.

Fixes: d60483fa ("arm64: dts: add description for solidrun am642 som and evaluation board")
Signed-off-by: Josua Mayer <josua@solid-run.com>
Link: https://lore.kernel.org/r/20240504-ti-rs485-rts-v1-1-e88ef1c96f34@solid-run.comSigned-off-by: Vignesh Raghavendra <vigneshr@ti.com>

arch/arm64/boot/dts/ti/k3-am642-hummingboard-t.dts

@@ -282,7 +282,6 @@ &main_uart3 {
 	pinctrl-names = "default";
 	pinctrl-0 = <&main_uart3_default_pins>;
 	uart-has-rtscts;
-	rs485-rts-active-low;
 	linux,rs485-enabled-at-boot-time;
 	status = "okay";
 };