drm_hwcomposer: Use shared pointer type for the pipeline_ variable

The change will help with resource management in further patches.

Signed-off-by: Roman Stratiienko <r.stratiienko@gmail.com>
diff --git a/drm/ResourceManager.h b/drm/ResourceManager.h
index 7fa3fc6..72ee3e2 100644
--- a/drm/ResourceManager.h
+++ b/drm/ResourceManager.h
@@ -34,8 +34,8 @@
 class PipelineToFrontendBindingInterface {
  public:
   virtual ~PipelineToFrontendBindingInterface() = default;
-  virtual bool BindDisplay(DrmDisplayPipeline *);
-  virtual bool UnbindDisplay(DrmDisplayPipeline *);
+  virtual bool BindDisplay(std::shared_ptr<DrmDisplayPipeline>);
+  virtual bool UnbindDisplay(std::shared_ptr<DrmDisplayPipeline>);
   virtual void FinalizeDisplayBinding();
 };
 
@@ -82,7 +82,7 @@
 
   std::recursive_mutex main_lock_;
 
-  std::map<DrmConnector *, std::unique_ptr<DrmDisplayPipeline>>
+  std::map<DrmConnector *, std::shared_ptr<DrmDisplayPipeline>>
       attached_pipelines_;
 
   PipelineToFrontendBindingInterface *const frontend_interface_;