i40e: don't allocate zero size

Shockingly, the compiler didn't flag this uninitialized variable. This
fixes a potential memory corruption condition where ARQ messages are
written to random memory locations.

Change-Id: Iac82f4562d2bf3f42df3f3b2163d9cbed2160135
Signed-off-by: Mitch Williams <mitch.a.williams@intel.com>
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Sibai Li <sibai.li@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/i40e/i40e_main.c

@@ -4492,6 +4492,7 @@ static void i40e_clean_adminq_subtask(struct i40e_pf *pf)
 	if (!test_bit(__I40E_ADMINQ_EVENT_PENDING, &pf->state))
 		return;
 
+	event.msg_size = I40E_MAX_AQ_BUF_SIZE;
 	event.msg_buf = kzalloc(event.msg_size, GFP_KERNEL);
 	if (!event.msg_buf)
 		return;