Linux: osi_TryEvictVCache: Don’t skip the first dentry if D_ALIAS_IS_HLIST

Linux: osi_TryEvictVCache: Don’t skip the first dentry if D_ALIAS_IS_HLIST

An hlist doesn’t begin with a sentinel like a list does, so the old
code would skip the first dentry or crash with a NULL dereference if
there wasn’t one.  Use the kernel’s list_for_each_entry or
hlist_for_each_entry macros instead of trying to do it manually.

Should fix a crash observed by Alex Chernyakhovsky on kernel 3.6 and
newer.

Change-Id: I6d7bd190013a0250ca896af8d5182df55a3376b0
Signed-off-by: Anders Kaseorg <andersk@mit.edu>
Reviewed-on: http://gerrit.openafs.org/9857
Reviewed-by: Alex Chernyakhovsky <achernya@mit.edu>
Tested-by: Alex Chernyakhovsky <achernya@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Marc Dionne <marc.c.dionne@gmail.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>