realtek: ZyXEL GS1900-48: fix system LED polarity

When driven by a GPIO pin, the system LED needs to be configured as
active high. Otherwise the LED switches off after booting and
initialisation.

Fixes: 47f5a0a ("realtek: Add support for ZyXEL GS1900-48 Switch")
Signed-off-by: Sander Vanheule <sander@svanheule.net>

target/linux/realtek/dts-5.10/rtl8393_zyxel_gs1900-48.dts

@@ -28,7 +28,7 @@
 
 		led_sys: sys {
 			label = "green:sys";
-			gpios = <&gpio0 0 GPIO_ACTIVE_LOW>;
+			gpios = <&gpio0 0 GPIO_ACTIVE_HIGH>;
 		};
 	};