video_core: Resolve more variable shadowing scenarios

Resolves variable shadowing scenarios up to the end of the OpenGL code
to make it nicer to review. The rest will be resolved in a following
commit.

src/video_core/gpu_synch.h

@@ -19,7 +19,7 @@ namespace VideoCommon {
 /// Implementation of GPU interface that runs the GPU synchronously
 class GPUSynch final : public Tegra::GPU {
 public:
-    explicit GPUSynch(Core::System& system, bool use_nvdec);
+    explicit GPUSynch(Core::System& system_, bool use_nvdec_);
     ~GPUSynch() override;
 
     void Start() override;