ufs_rename(): fix bogus argument of folio_release_kmap()

new_dir does *NOT* point into dir_folio - it's an inode, not a pointer
to ufs directory entry.

Fixes: 516b97cf "ufs: Convert directory handling to kmap_local"
Acked-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>