cachefiles: fix incorrect dentry refcount in cachefiles_cull()

In the Linux kernel, the following vulnerability has been resolved: cachefiles: fix incorrect dentry refcount in cachefiles_cull() The patch mentioned below changed cachefiles_bury_object() to expect 2 references to the 'rep' dentry. Three of the callers were changed to use start_removing_dentry() which takes an extra reference so in those cases the call gets the expected references. However there is another call to cachefiles_bury_object() in cachefiles_cull() which did not need to be changed to use start_removing_dentry() and so was not properly considered. It still passed the dentry with just one reference so the net result is that a reference is lost. To meet the expectations of cachefiles_bury_object(), cachefiles_cull() must take an extra reference before the call. It will be dropped by cachefiles_bury_object().