add class for submenu of 'Ventoy UEFI Utilities'

INSTALL/grub/debug.cfg

@@ -148,7 +148,7 @@ submenu "Screen Display Mode" --class=debug_screen_mode {
 
 if [ "$grub_platform" != "pc" ]; then
     submenu 'Ventoy UEFI Utilities' --class=debug_util {
-        menuentry 'Fixup Windows BlinitializeLibrary Failure' {
+        menuentry 'Fixup Windows BlinitializeLibrary Failure' --class=debug_util_blinit {
             chainloader ${vtoy_path}/vtoyutil_x64.efi env_param=${env_param} ${vtdebug_flag} feature=fix_windows_mmap
             boot
             echo -e "\npress ENTER to exit ..."