Fix resource leaks in drm hal

bug:36408047
test: manual testing to verify leaks are fixed
Change-Id: I3ade65eff4bbe8603fe4cf04b00ab1f3e1122f90
diff --git a/drm/libmediadrm/DrmHal.cpp b/drm/libmediadrm/DrmHal.cpp
index 3596f12..f54954a 100644
--- a/drm/libmediadrm/DrmHal.cpp
+++ b/drm/libmediadrm/DrmHal.cpp
@@ -410,6 +410,7 @@
     }
 
     setListener(NULL);
+    mPlugin->setListener(NULL);
     mPlugin.clear();
 
     return OK;