ARM: dts: stm32: use IRQ_TYPE_EDGE_FALLING on stm32mp157c-dk2

Replace the number 2 with the appropriate numerical constant defined in
dt-bindings/interrupt-controller/irq.h.

Signed-off-by: Dario Binacchi <[e-mail]>
Reviewed-by: Antonio Borneo <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexandre Torgue <[e-mail]>

arch/arm/boot/dts/st/stm32mp157c-dk2.dts

···
 	touchscreen@38 {
 		compatible = "focaltech,ft6236";
 		reg = <0x38>;
-		interrupts = <2 2>;
+		interrupts = <2 IRQ_TYPE_EDGE_FALLING>;
 		interrupt-parent = <&gpiof>;
 		touchscreen-size-x = <480>;
 		touchscreen-size-y = <800>;