drm_hwcomposer: fix buffer leak when using the GL compositor inside DrmDisplayCompositor

Change-Id: Id3a6deea9fc0f97640b34dacb25d36f3793f2d4e
diff --git a/drmdisplaycomposition.cpp b/drmdisplaycomposition.cpp
index 21a9c2a..c76a23c 100644
--- a/drmdisplaycomposition.cpp
+++ b/drmdisplaycomposition.cpp
@@ -171,4 +171,8 @@
 uint32_t DrmDisplayComposition::dpms_mode() const {
   return dpms_mode_;
 }
+
+Importer *DrmDisplayComposition::importer() const {
+  return importer_;
+}
 }