block/sheepdog: code beautification

No functional changes, just whitespace manipulation.

Signed-off-by: Jeff Cody <jcody@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Signed-off-by: Jeff Cody <jcody@redhat.com>