platform/x86: alienware-wmi: Remove unnecessary check at module exit

platform/x86: alienware-wmi: Remove unnecessary check at module exit

Module initialization fails if platform device fails to register so it's
always not NULL at exit.

Reviewed-by: Armin Wolf <W_Armin@gmx.de>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Kurt Borja <kuurtb@gmail.com>
Link: https://lore.kernel.org/r/20250105153019.19206-3-kuurtb@gmail.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>