staging/lustre/mdc: Initialize req in mdc_enqueue for !it case

Commit ab909585 ("staging: lustre: Cleanup variable declarations
in mdc_enqueue()") broke Lustre flock handling introducing access
to uninitialized req variable, leading to bizzare crash in a later
call to __req_capsule_offset with invalid pill value.

Set req to NULL just for this case as in all other cases req is
explicitly initialized with request packing call.
Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
CC: Srikrishan Malik <srikrishanmalik@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lustre/mdc/mdc_locks.c

@@ -828,6 +828,7 @@ int mdc_enqueue(struct obd_export *exp, struct ldlm_enqueue_info *einfo,
 			 einfo->ei_type);
 		policy = (ldlm_policy_data_t *)lmm;
 		res_id.name[3] = LDLM_FLOCK;
+		req = NULL;
 	} else if (it->it_op & IT_OPEN) {
 		req = mdc_intent_open_pack(exp, it, op_data, lmm, lmmsize,
 					   einfo->ei_cbdata);