staging/lustre/libcfs: fix illegal page access of tracefiled()

After failure happens and put_pages_back() returns the pages,
tracefiled() should not go on itering on the page list.
Otherwise, some pages might be accessed illegally.

Signed-off-by: Li Xi <lixi@ddn.com>
Signed-off-by: Jian Yu <jian.yu@intel.com>
Reviewed-on: http://review.whamcloud.com/11454
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-5126


Reviewed-by: Emoly Liu <emoly.liu@intel.com>
Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>