platform/x86: think-lmi: Fix reference leak

In the Linux kernel, the following vulnerability has been resolved: platform/x86: think-lmi: Fix reference leak If a duplicate attribute is found using kset_find_obj(), a reference to that attribute is returned which needs to be disposed accordingly using kobject_put(). Move the setting name validation into a separate function to allow for this change without having to duplicate the cleanup code for this setting. As a side note, a very similar bug was fixed in commit 7295a996fdab ("platform/x86: dell-sysman: Fix reference leak"), so it seems that the bug was copied from that driver. Compile-tested only.