Fix nyx_device_close memory deallocations

- free name and description using g_free (allocated using g_strndup)
- cleanup logic by caching whole nyx_device struct instead of
  picking individual members

Open-webOS-DCO-1.0-Signed-off-by: Janne Kiiski <janne.kiiski@palm.com>

Change-Id: I9ce32cd8dd80daf93f260cd54aabe7df58835196