LU-4082 llite: Chk ret of ll_prep_md_op_data in ll_dir_filler

LU-4082 llite: Chk ret of ll_prep_md_op_data in ll_dir_filler

ll_dir_filler() now checks the returned pointer from
ll_prep_md_op_data() using IS_ERR()

Signed-off-by: Swapnil Pimpale <spimpale@ddn.com>
Change-Id: Ia4321db2ca9dddaa4487f62544de10239120bad3
Reviewed-on: http://review.whamcloud.com/8073
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Tested-by: Jenkins
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>