i40e: Fix log TC creation failure when max num of queues is exceeded

Fix missing failed message if driver does not have enough queues to
complete TC command. Without this fix no message is displayed in dmesg.

Fixes: a9ce82f7 ("i40e: Enable 'channel' mode in mqprio for TC configs")
Signed-off-by: Grzegorz Szczurek <grzegorzx.szczurek@intel.com>
Signed-off-by: Jedrzej Jagielski <jedrzej.jagielski@intel.com>
Tested-by: Imam Hassan Reza Biswas <imam.hassan.reza.biswas@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

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

@@ -7290,6 +7290,8 @@ static int i40e_validate_mqprio_qopt(struct i40e_vsi *vsi,
 	}
 	if (vsi->num_queue_pairs <
 	    (mqprio_qopt->qopt.offset[i] + mqprio_qopt->qopt.count[i])) {
+		dev_err(&vsi->back->pdev->dev,
+			"Failed to create traffic channel, insufficient number of queues.\n");
 		return -EINVAL;
 	}
 	if (sum_max_rate > i40e_get_link_speed(vsi)) {