LU-13805 clio: Trivial DIO cleanups

LU-13805 clio: Trivial DIO cleanups

This is some minor DIO refactoring and an additional debug
message discovered while working on this.  Extremely minor.

test-parameters: trivial

Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: Ica2a7340ac02d3ba0d8f65662ff4b39026078e81
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/49987
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>