cachefiles: fix incorrect dentry refcount in cachefiles_cull()

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().

Reported-by: Marc Dionne <marc.dionne@auristor.com>
Fixes: 7bb1eb45e43c ("VFS: introduce start_removing_dentry()")
Signed-off-by: NeilBrown <neil@brown.name>
Link: https://patch.msgid.link/177456350181.1851489.16359967086642190170@noble.neil.brown.name
Acked-by: Paulo Alcantara (Red Hat) <pc@manguebit.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>