riscv: Use of_get_cpu_hwid()

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

Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: linux-riscv@lists.infradead.org
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211006164332.1981454-9-robh@kernel.org

arch/riscv/kernel/cpu.c

@@ -22,7 +22,8 @@ int riscv_of_processor_hartid(struct device_node *node)
 		return -ENODEV;
 	}
 
-	if (of_property_read_u32(node, "reg", &hart)) {
+	hart = of_get_cpu_hwid(node, 0);
+	if (hart == ~0U) {
 		pr_warn("Found CPU without hart ID\n");
 		return -ENODEV;
 	}