eCryptfs: use list_for_each_entry_safe() when wiping auth toks

Use list_for_each_entry_safe() when wiping the authentication token list.

Signed-off-by: Michael Halcrow <mhalcrow@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>