iavf: Fix error handling in iavf_init_module()

The iavf_init_module() won't destroy workqueue when pci_register_driver()
failed. Call destroy_workqueue() when pci_register_driver() failed to
prevent the resource leak.

Similar to the handling of u132_hcd_init in commit f276e002
("usb: u132-hcd: fix resource leak")

Fixes: 2803b16c ("i40e/i40evf: Use private workqueue")
Signed-off-by: Yuan Can <yuancan@huawei.com>
Tested-by: Konrad Jankowski <konrad0.jankowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

drivers/net/ethernet/intel/iavf/iavf_main.c

@@ -5196,6 +5196,8 @@ static struct pci_driver iavf_driver = {
  **/
 static int __init iavf_init_module(void)
 {
+	int ret;
+
 	pr_info("iavf: %s\n", iavf_driver_string);
 
 	pr_info("%s\n", iavf_copyright);
@@ -5206,7 +5208,12 @@ static int __init iavf_init_module(void)
 		pr_err("%s: Failed to create workqueue\n", iavf_driver_name);
 		return -ENOMEM;
 	}
-	return pci_register_driver(&iavf_driver);
+
+	ret = pci_register_driver(&iavf_driver);
+	if (ret)
+		destroy_workqueue(iavf_wq);
+
+	return ret;
 }
 
 module_init(iavf_init_module);