staging: lustre: llite: check ret of ll_prep_md_op_data in ll_dir_filler

staging: lustre: llite: check 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>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-4082
Reviewed-on: http://review.whamcloud.com/8073
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>