fix copy assignment signatures

get value by reference

introduced in
commit 8c2f2e1d and
commit f9b200ce

Change-Id: Iba84dd752f4cbdde9f3676c434d107efabe63a38
Reviewed-on: https://gerrit.libreoffice.org/23974Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>

basctl/source/basicide/doceventnotifier.cxx

@@ -67,7 +67,7 @@ namespace basctl
     public:
         // noncopyable
         Impl(const Impl&) = delete;
-        const Impl& operator=(const Impl) = delete;
+        Impl& operator=(const Impl&) = delete;
 
         Impl (DocumentEventListener&, Reference<XModel> const& rxDocument);
         virtual ~Impl ();

canvas/source/directx/dx_graphicsprovider.hxx

@@ -36,7 +36,7 @@ namespace dxcanvas
         virtual ~GraphicsProvider() {}
         /// make noncopyable
         GraphicsProvider(const GraphicsProvider&) = delete;
-        const GraphicsProvider operator=(const GraphicsProvider) = delete;
+        GraphicsProvider& operator=(const GraphicsProvider&) = delete;
 
         virtual GraphicsSharedPtr getGraphics() = 0;
     };