powerpc/powermac: Add missing of_node_put() in smp_core99_setup()

In smp_core99_setup(), add of_node_put() to drop the reference once it's
no longer needed.

Signed-off-by: Liang He <windhl@126.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220620150518.4074910-1-windhl@126.com

arch/powerpc/platforms/powermac/smp.c

@@ -711,6 +711,7 @@ static void __init smp_core99_setup(int ncpus)
 			printk(KERN_INFO "Processor timebase sync using"
 			       " platform function\n");
 		}
+		of_node_put(cpus);
 	}
 
 #else /* CONFIG_PPC64 */