csky: Use of_get_cpu_hwid()

Replace open coded parsing of CPU nodes 'reg' property with
of_get_cpu_hwid().

Cc: Guo Ren <guoren@kernel.org>
Cc: linux-csky@vger.kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211006164332.1981454-6-robh@kernel.org

arch/csky/kernel/smp.c

@@ -180,15 +180,13 @@ void __init setup_smp_ipi(void)
 void __init setup_smp(void)
 {
 	struct device_node *node = NULL;
-	int cpu;
+	unsigned int cpu;
 
 	for_each_of_cpu_node(node) {
 		if (!of_device_is_available(node))
 			continue;
 
-		if (of_property_read_u32(node, "reg", &cpu))
-			continue;
-
+		cpu = of_get_cpu_hwid(node, 0);
 		if (cpu >= NR_CPUS)
 			continue;