kernfs: Rename kernfs_put_open_node to kernfs_unlink_open_file.

Since we are no longer using refcnt for kernfs_open_node instances, rename
kernfs_put_open_node to kernfs_unlink_open_file to reflect this change.
Also update function description and inline comments accordingly.

Signed-off-by: Imran Khan <imran.f.khan@oracle.com>
Link: https://lore.kernel.org/r/20220504095123.295859-2-imran.f.khan@oracle.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>