dir: verified pathnames fallout

dir: verified pathnames fallout

Fix some issues introduced with the verified directory path names
commit in master:
- In GetVerifiedBlob, the output parameter is set to NULL on entry
and dereferenced later on.
- For Linux, the code in afs_linux_readdir was changed to pass a
DirEntry to GetVerifiedBlob.  This is incorrect, the function still
expects a DirBuffer pointer.
- In afs_dir_IsEmpty, the assignment of ep was removed, leaving
the function to dereference this pointer which was never set.

Change-Id: I9045076ebe636cf68c19487c0d58baebf2de7dd1
Reviewed-on: http://gerrit.openafs.org/5292
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>