dm vdo dedupe: fix various small nits

Remove extra blank line, mark function inline, add missing
braces, and fix a typo in a comment.

Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Signed-off-by: Chung Chung <cchung@redhat.com>
Signed-off-by: Matthew Sakai <msakai@redhat.com>