staging/lustre/mdc: fix issue found by Klocwork Insight tool

staging/lustre/mdc: fix issue found by Klocwork Insight tool

Pointer 'mod' checked for NULL at line 160 may be dereferenced at line 208.

Signed-off-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-on: http://review.whamcloud.com/9387
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-4629
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>