savevm: Add DeviceState param

When available, we'd like to be able to access the DeviceState
when registering a savevm.  For buses with a get_dev_path()
function, this will allow us to create more unique savevm
id strings.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/exec.c b/exec.c
index a6b3f21..c8be508 100644
--- a/exec.c
+++ b/exec.c
@@ -641,8 +641,8 @@
     cpu_list_unlock();
 #endif
 #if defined(CPU_SAVE_VERSION) && !defined(CONFIG_USER_ONLY)
-    vmstate_register(cpu_index, &vmstate_cpu_common, env);
-    register_savevm("cpu", cpu_index, CPU_SAVE_VERSION,
+    vmstate_register(NULL, cpu_index, &vmstate_cpu_common, env);
+    register_savevm(NULL, "cpu", cpu_index, CPU_SAVE_VERSION,
                     cpu_save, cpu_load, env);
 #endif
 }