[UI] Update gamertag input field only on change

No need to validate gamertag every frame

src/xenia/kernel/xam/ui/create_profile_ui.h

@@ -35,6 +35,7 @@ class CreateProfileUI final : public XamDialog {
   bool has_opened_ = false;
   bool migration_ = false;
   char gamertag_[16] = "";
+  bool valid_gamertag_ = false;
   Emulator* emulator_;
 };