Cite correct hook in _post_formats_fix_empty_title() docs

[DrewAPicture]

_post_formats_fix_empty_title() hooks to the wp_insert_post_data filter not the save_post hook. Patch corrects the inline docs.

[SergeyBiryukov]

[24043] leaves a false impression that wp_insert_post_data is an action.

We should make it clear that it's a filter: 24303.2.diff​.

[DrewAPicture]

Works for me. Shouldn't be any adverse affects to moving the hook, correct?

[SergeyBiryukov]

In 24233:

Update _post_formats_fix_empty_title() description. Make it clear that 'wp_insert_post_data' is a filter, not an action. props DrewAPicture. fixes #24303.

[kovshenin]

Good catch!