dt-bindings: can: mcp251x: change example interrupt type to IRQ_TYPE_LEVEL_LOW

The MCP2515 datasheet clearly describes a level-triggered interrupt pin.
Change example bindings accordingly.

Link: https://lore.kernel.org/r/20200915223527.1417033-25-mkl@pengutronix.deSigned-off-by: NMarc Kleine-Budde <mkl@pengutronix.de>

Documentation/devicetree/bindings/net/can/microchip,mcp251x.txt

@@ -19,7 +19,7 @@ Example:
 		reg = <1>;
 		clocks = <&clk24m>;
 		interrupt-parent = <&gpio4>;
-		interrupts = <13 0x2>;
+		interrupts = <13 IRQ_TYPE_LEVEL_LOW>;
 		vdd-supply = <&reg5v0>;
 		xceiver-supply = <&reg5v0>;
 	};