platform/x86: ideapad-laptop: Use str_on_off() helper

platform/x86: ideapad-laptop: Use str_on_off() helper

Use the str_on_off() helper instead of open-coding the same operation.
This improves code readability.

No functional change intended.

Suggested-by: kernel test robot <lkp@intel.com>
Suggested-by: Julia Lawall <julia.lawall@inria.fr>
Link: https://lore.kernel.org/r/202510311551.xjWbHTrm-lkp@intel.com/
Suggested-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/2bae2ea7-2ef9-0cfa-0c2c-39a7043b2aa5@linux.intel.com/
Signed-off-by: Rong Zhang <i@rong.moe>
Link: https://patch.msgid.link/20251105182832.104946-2-i@rong.moe
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>