gl_rasterizer: Minor cleanup

Minor code cleanup from unaddressed feedback in #1654

src/video_core/engines/maxwell_3d.cpp

@@ -121,10 +121,8 @@ void Maxwell3D::WriteReg(u32 method, u32 value, u32 remaining_params) {
         debug_context->OnEvent(Tegra::DebugContext::Event::MaxwellCommandLoaded, nullptr);
     }
 
-    u32 old = regs.reg_array[method];
-    regs.reg_array[method] = value;
-
-    if (value != old) {
+    if (regs.reg_array[method] != value) {
+        regs.reg_array[method] = value;
         if (method >= MAXWELL3D_REG_INDEX(vertex_attrib_format) &&
             method < MAXWELL3D_REG_INDEX(vertex_attrib_format) + regs.vertex_attrib_format.size()) {
             dirty_flags.vertex_attrib_format = true;