namei: tweak getlinkbyte error handling

namei: tweak getlinkbyte error handling

in the event of a pread error, add the same error exit path
trigger that we have elsewhere

Reviewed-on: http://gerrit.openafs.org/5843
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Reviewed-by: Jeffrey Altman <jaltman@secure-endpoints.com>
Tested-by: Jeffrey Altman <jaltman@secure-endpoints.com>
(cherry picked from commit 51f71e533b20cd875eec8adda71edea044a606da)

Change-Id: I05623d392e7e3446b7b41dcc1778c6aca986bca1
Reviewed-on: http://gerrit.openafs.org/6078
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>