eCryptfs: use after free in ecryptfs_release_messaging()

We're freeing the list iterator so we should be using the _safe()
version of hlist_for_each_entry().

Fixes: 88b4a07e ("[PATCH] eCryptfs: Public key transport mechanism")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>