platform/x86: dell-wmi-sysman: Fix class device unregistration

Devices under the firmware_attributes_class do not have unique a dev_t.
Therefore, device_unregister() should be used instead of
device_destroy(), since the latter may match any device with a given
dev_t.

Fixes: e8a60aa ("platform/x86: Introduce support for Systems Management Driver over WMI for Dell Systems")
Signed-off-by: Kurt Borja <kuurtb@gmail.com>
Link: https://lore.kernel.org/r/20250625-dest-fix-v1-3-3a0f342312bb@gmail.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

Author: kuu-rt

drivers/platform/x86/dell/dell-wmi-sysman/sysman.c

@@ -597,7 +597,7 @@ static int __init sysman_init(void)
 	release_attributes_data();
 
 err_destroy_classdev:
-	device_destroy(&firmware_attributes_class, MKDEV(0, 0));
+	device_unregister(wmi_priv.class_dev);
 
 err_exit_bios_attr_pass_interface:
 	exit_bios_attr_pass_interface();
@@ -611,7 +611,7 @@ static int __init sysman_init(void)
 static void __exit sysman_exit(void)
 {
 	release_attributes_data();
-	device_destroy(&firmware_attributes_class, MKDEV(0, 0));
+	device_unregister(wmi_priv.class_dev);
 	exit_bios_attr_set_interface();
 	exit_bios_attr_pass_interface();
 }