PCI: endpoint: Fix a potential NULL pointer dereference

In case alloc_workqueue() fails, return -ENOMEM to avoid
potential NULL pointer dereferences.
Signed-off-by: Kangjie Lu <kjlu@umn.edu>
[lorenzo.pieralisi@arm.com: commit log and code update]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>

drivers/pci/endpoint/functions/pci-epf-test.c

@@ -591,6 +591,11 @@ static int __init pci_epf_test_init(void)
 
 	kpcitest_workqueue = alloc_workqueue("kpcitest",
 					     WQ_MEM_RECLAIM | WQ_HIGHPRI, 0);
+	if (!kpcitest_workqueue) {
+		pr_err("Failed to allocate the kpcitest work queue\n");
+		return -ENOMEM;
+	}
+
 	ret = pci_epf_register_driver(&test_driver);
 	if (ret) {
 		pr_err("Failed to register pci epf test driver --> %d\n", ret);