Show correct post format name in adjacent post links

Without passing a post object to `get_post_format()`, WP relies on the global `$post` variable. As a result, the adjacent post links on a single post are prepended with the format name of the post being viewed, not the respective formats of the adjacent posts.

Since the adjacent post's `$post` object is available in the `publish_post_format_title()` function, passing it to `get_post_format()` ensures that the proper format name appears in the adjacent post links.