vhost: coding style and flush cleanups

[Mike Christie]

The following patches apply over linus's tree and mst's vhost branch.
The patches are just some flush cleanups and a patch to reduce flush
calls and some coding style fixups.

My worker threading patches are built over these patches, but they seem
like patches that would be ok even if the threading patches never get
merged, so I've broken them out to make the threading patchset easier to
review.

V2:
- Added vhost_work coding style cleanup patch. The worker threading
patchset modifies that code. I thought I would clean it up since my
patch that added a new field looked weird using different styles.