Restore return statement that went missing. (project-chip#20087)

The changes in project-chip#19870
incorrectly removed a return here.  Now we'll fall through to the cases that
assume the proxy is not in a connected state to start with, which is not
desirable.

src/controller/CHIPDeviceController.cpp

@@ -335,6 +335,7 @@ CHIP_ERROR DeviceController::DisconnectDevice(NodeId nodeId)
     if (proxy->IsConnected())
     {
         proxy->Disconnect();
+        return CHIP_NO_ERROR;
     }
 
     if (proxy->IsConnecting())