tests: vmstate static checker: add substructure for usb-kbd for hid section

This shows how the script deals with substructures added to vmstate
descriptions that don't change the on-wire format.
Signed-off-by: NAmit Shah <amit.shah@redhat.com>
Reviewed-by: NJuan Quintela <quintela@redhat.com>
Signed-off-by: NJuan Quintela <quintela@redhat.com>

tests/vmstate-static-checker-data/dump2.json

@@ -844,7 +844,7 @@
           "field": "dev",
           "version_id": 0,
           "field_exists": false,
-          "size": 4352,
+          "size": 5832,
           "Description": {
             "name": "USBDevice",
             "version_id": 1,
@@ -895,6 +895,16 @@
             ]
           }
         },
+        {
+          "field": "hid",
+          "version_id": 0,
+          "field_exists": false,
+          "size": 312,
+          "Description": {
+            "name": "HIDKeyboardDevice",
+            "version_id": 1,
+            "minimum_version_id": 1,
+            "Fields": [
               {
                 "field": "kbd.keycodes",
                 "version_id": 0,
@@ -952,4 +962,7 @@
             ]
           }
         }
+      ]
+    }
+  }
 }