LU-5997 mdd: initialize mdd's obd->obd_vars

LU-5997 mdd: initialize mdd's obd->obd_vars

mdd_procfs_init() initializes obd->obd_vars of not mdd's obd, but
mdt's one. Having mdd's obd->obd_vars uninitialized leads conf_param
to fail on setting mdd' parametes.

Xyratex-bug-id: MRP-2277
Signed-off-by: Vladimir Saveliev <vladimir.saveliev@seagate.com>
Change-Id: I065dc9e4577816ce08f22787116fae4f7e971db5
Reviewed-on: http://review.whamcloud.com/12980
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Simmons <uja.ornl@gmail.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>