ARM: rockchip: Fix use of plain integer as NULL pointer

This fixes the following sparse build warning:

     mach-rockchip/platsmp.c:68:43: Using plain integer as NULL pointer
Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

arch/arm/mach-rockchip/platsmp.c

@@ -65,7 +65,7 @@ static struct reset_control *rockchip_get_core_reset(int cpu)
 	if (dev)
 		np = dev->of_node;
 	else
-		np = of_get_cpu_node(cpu, 0);
+		np = of_get_cpu_node(cpu, NULL);
 
 	return of_reset_control_get(np, NULL);
 }