Fix pipeline shader compilation errors

Fixed two GLSL compilation errors for AMD drivers, closing issue #14 (closed)

pipeline/glow-extras/pipeline/RenderPipeline.cc

@@ -312,7 +312,7 @@ void glow::pipeline::RenderPipeline::GlobalInit()
                         return res;
                     }
 
-                    const PipelineSceneUnpacked gPipelineScene = unpackPipelineSceneUbo();
+                    PipelineSceneUnpacked gPipelineScene = unpackPipelineSceneUbo();
                     #endif
                 )");
             return true;