libafs: avoid contaminating the return of lookup vnop

when we resort to checking the inlinebulk errors to see if a retry
is needed, do not overwrite the lookup return code; only decide if
a retry is needed.

problem case was where the first vnode returned EACCES and so
all vnodes were assumed to have failed, when just one did.

Change-Id: Ifd7361ce5af50a72817afa81d31d9cfbda906efd
Reviewed-on: http://gerrit.openafs.org/11537
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>