dm vdo delta-index: fix various small nits

Fix some needless line wrapping (given surrounding context), missing
braces and some stale or incorrect references to data structure or
function name.

Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Signed-off-by: Susan LeGendre-McGhee <slegendr@redhat.com>
Signed-off-by: Matthew Sakai <msakai@redhat.com>