ixgbevf: Fix resource leak in ixgbevf_init_module()

ixgbevf_init_module() won't destroy the workqueue created by
create_singlethread_workqueue() when pci_register_driver() failed. Add
destroy_workqueue() in fail path to prevent the resource leak.

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

Fixes: 40a13e24 ("ixgbevf: Use a private workqueue to avoid certain possible hangs")
Signed-off-by: Shang XiaoJing <shangxiaojing@huawei.com>
Reviewed-by: Saeed Mahameed <saeed@kernel.org>
Tested-by: Konrad Jankowski <konrad0.jankowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c

@@ -4869,6 +4869,8 @@ static struct pci_driver ixgbevf_driver = {
  **/
 static int __init ixgbevf_init_module(void)
 {
+	int err;
+
 	pr_info("%s\n", ixgbevf_driver_string);
 	pr_info("%s\n", ixgbevf_copyright);
 	ixgbevf_wq = create_singlethread_workqueue(ixgbevf_driver_name);
@@ -4877,7 +4879,13 @@ static int __init ixgbevf_init_module(void)
 		return -ENOMEM;
 	}
 
-	return pci_register_driver(&ixgbevf_driver);
+	err = pci_register_driver(&ixgbevf_driver);
+	if (err) {
+		destroy_workqueue(ixgbevf_wq);
+		return err;
+	}
+
+	return 0;
 }
 
 module_init(ixgbevf_init_module);