gl_state: Remove unnecessary const specifier on Apply

src/video_core/renderer_opengl/gl_state.cpp

@@ -43,7 +43,7 @@ OpenGLState::OpenGLState() {
     draw.shader_program = 0;
 }
 
-const void OpenGLState::Apply() {
+void OpenGLState::Apply() {
     // Culling
     if (cull.enabled != cur_state.cull.enabled) {
         if (cull.enabled) {

src/video_core/renderer_opengl/gl_state.h

@@ -63,7 +63,7 @@ public:
     }
     
     /// Apply this state as the current OpenGL state
-    const void Apply();
+    void Apply();
 
 private:
     static OpenGLState cur_state;