afs: refactor afs_linux_dentry_revalidate

afs: refactor afs_linux_dentry_revalidate

No functional change.   Separate the

  if (locked && vcp->mvstat == 1) { ... }

conditional into

  if (locked) {
    if (vcp->mvstat == 1) { ... }
  }

in preparation for another change.

Change-Id: I1fe42ed7771882ce365d9359a4e6187c283592a8
Reviewed-on: http://gerrit.openafs.org/11692
Reviewed-by: Perry Ruiter <pruiter@sinenomine.net>
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>