platform/x86: dell-sysman: Fix reference leak

platform/x86: dell-sysman: Fix reference leak

If a duplicate attribute is found using kset_find_obj(),
a reference to that attribute is returned. This means
that we need to dispose it accordingly. Use kobject_put()
to dispose the duplicate attribute in such a case.

Compile-tested only.

Fixes: e8a60aa7404b ("platform/x86: Introduce support for Systems Management Driver over WMI for Dell Systems")
Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Link: https://lore.kernel.org/r/20230805053610.7106-1-W_Armin@gmx.de
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>