dtoverlays: ili251x: Replace incorrect comment on irq trigger

The comment said "high-to-low edge triggered", but used a value
of 8 which is IRQ_TYPE_LEVEL_LOW.

Update to use the define.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>

arch/arm/boot/dts/overlays/ilitek251x-overlay.dts

@@ -2,6 +2,8 @@
 /dts-v1/;
 /plugin/;
 
+#include <dt-bindings/interrupt-controller/irq.h>
+
  / {
 	compatible = "brcm,bcm2835";
 
@@ -29,7 +31,7 @@
 				pinctrl-names = "default";
 				pinctrl-0 = <&ili251x_pins>;
 				interrupt-parent = <&gpio>;
-				interrupts = <4 8>; // high-to-low edge triggered
+				interrupts = <4 IRQ_TYPE_LEVEL_LOW>;
 				touchscreen-size-x = <16384>;
 				touchscreen-size-y = <9600>;
 			};