fix a minor copy-paste mistake from earlier commit

Author: cowtowncoder

src/main/java/com/fasterxml/jackson/databind/type/ResolvedRecursiveType.java

@@ -50,15 +50,15 @@ public StringBuilder getGenericSignature(StringBuilder sb) {
         if (_referencedType != null) {
             return _referencedType.getGenericSignature(sb);
         }
-        return _referencedType.getGenericSignature(sb);
+        return sb.append("?");
     }
 
     @Override
     public StringBuilder getErasedSignature(StringBuilder sb) {
         if (_referencedType != null) {
             return _referencedType.getErasedSignature(sb);
         }
-        return _referencedType.getErasedSignature(sb);
+        return sb;
     }
 
     @Override