x86: mp_init: Switch to livetree

Update this code to use livetree calls instead of flat-tree.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Wolfgang Wallner <wolfgang.wallner@br-automation.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/arch/x86/cpu/mp_init.c b/arch/x86/cpu/mp_init.c
index 7fde4ff..c25d17c 100644
--- a/arch/x86/cpu/mp_init.c
+++ b/arch/x86/cpu/mp_init.c
@@ -507,8 +507,7 @@
 	 * seq num in the uclass_resolve_seq() during device_probe(). To avoid
 	 * this, set req_seq to the reg number in the device tree in advance.
 	 */
-	cpu->req_seq = fdtdec_get_int(gd->fdt_blob, dev_of_offset(cpu), "reg",
-				      -1);
+	cpu->req_seq = dev_read_u32_default(cpu, "reg", -1);
 	plat->ucode_version = microcode_read_rev();
 	plat->device_id = gd->arch.x86_device;