machine: Fix coding style at machine_run_board_init()

Commit 7747abf1 ("hw/machine: Remove the Zero check of
nb_numa_nodes for numa_complete_configuration()") removed the
curly brackets.  Re-add them.
Signed-off-by: NDou Liyang <douly.fnst@cn.fujitsu.com>
Message-Id: <20180710105129.23296-1-douly.fnst@cn.fujitsu.com>
Reviewed-by: NIgor Mammedov <imammedo@redhat.com>
[ehabkost: rewrote commit message]
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>

hw/core/machine.c

@@ -793,8 +793,9 @@ void machine_run_board_init(MachineState *machine)
     MachineClass *machine_class = MACHINE_GET_CLASS(machine);
 
     numa_complete_configuration(machine);
-    if (nb_numa_nodes)
+    if (nb_numa_nodes) {
         machine_numa_finish_cpu_init(machine);
+    }
 
     /* If the machine supports the valid_cpu_types check and the user
      * specified a CPU with -cpu check here that the user CPU is supported.