Make ParameterValueSpecification reference consistent (#18598)

Author: joshuaz93

specification/synapse/data-plane/Microsoft.Synapse/preview/2021-12-01-preview/linkConnections.json

@@ -899,7 +899,10 @@
     },
     "ParameterValueSpecification": {
       "description": "An object mapping parameter names to argument values.",
-      "type": "object"
+      "type": "object",
+      "additionalProperties": {
+        "type": "object"
+      }
     }
   },
   "parameters": {