nstree: fix kernel-doc comments for internal functions

Documentation build reported:

  Warning: kernel/nstree.c:325 function parameter 'ns_tree' not described in '__ns_tree_adjoined_rcu'
  Warning: kernel/nstree.c:325 expecting prototype for ns_tree_adjoined_rcu(). Prototype was for __ns_tree_adjoined_rcu() instead
  Warning: kernel/nstree.c:353 expecting prototype for ns_tree_gen_id(). Prototype was for __ns_tree_gen_id() instead

The kernel-doc comments for `__ns_tree_adjoined_rcu()` and
`__ns_tree_gen_id()` had mismatched function names and a missing
parameter description. This patch updates the function names in the
kernel-doc headers and adds the missing `@ns_tree` parameter description
for `__ns_tree_adjoined_rcu()`.

Fixes: 885fc8a ("nstree: make iterator generic")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202511061542.0LO7xKs8-lkp@intel.com
Signed-off-by: Kriish Sharma <kriish.sharma2006@gmail.com>
Link: https://patch.msgid.link/20251111112533.2254432-1-kriish.sharma2006@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: KRIISHSHARMA

kernel/nstree.c

@@ -353,9 +353,10 @@ struct ns_common *ns_tree_lookup_rcu(u64 ns_id, int ns_type)
 }
 
 /**
- * ns_tree_adjoined_rcu - find the next/previous namespace in the same
+ * __ns_tree_adjoined_rcu - find the next/previous namespace in the same
  * tree
  * @ns: namespace to start from
+ * @ns_tree: namespace tree to search in
  * @previous: if true find the previous namespace, otherwise the next
  *
  * Find the next or previous namespace in the same tree as @ns. If
@@ -379,7 +380,7 @@ struct ns_common *__ns_tree_adjoined_rcu(struct ns_common *ns,
 }
 
 /**
- * ns_tree_gen_id - generate a new namespace id
+ * __ns_tree_gen_id - generate a new namespace id
  * @ns: namespace to generate id for
  * @id: if non-zero, this is the initial namespace and this is a fixed id
  *