path: add cleanup helper

path: add cleanup helper

Add a simple cleanup helper so we can cleanup struct path easily.
No need for any extra machinery. Avoid DEFINE_FREE() as it causes a
local copy of struct path to be used. Just rely on path_put() directly
called from a cleanup helper.

Link: https://lore.kernel.org/r/20240607-vfs-listmount-reverse-v1-2-7877a2bfa5e5@kernel.org
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>