audit: destroy long filenames correctly

filename should be destroyed via final_putname() instead of __putname()
Otherwise this result in following BUGON() in case of long names:
  kernel BUG at mm/slab.c:3006!
  Call Trace:
  kmem_cache_free+0x1c1/0x850
  audit_putname+0x88/0x90
  putname+0x73/0x80
  sys_symlinkat+0x120/0x150
  sys_symlink+0x16/0x20
  system_call_fastpath+0x16/0x1b

Introduced-in: 7950e3852

Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Eric Paris <eparis@redhat.com>