PCI: endpoint: Make ->remove() callback optional

Make ->remove() callback optional so that endpoint function drivers don't
have to populate empty ->remove() callback functions.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

drivers/pci/endpoint/pci-epf-core.c

@@ -333,11 +333,12 @@ static int pci_epf_device_probe(struct device *dev)
 
 static int pci_epf_device_remove(struct device *dev)
 {
-	int ret;
+	int ret = 0;
 	struct pci_epf *epf = to_pci_epf(dev);
 	struct pci_epf_driver *driver = to_pci_epf_driver(dev->driver);
 
-	ret = driver->remove(epf);
+	if (driver->remove)
+		ret = driver->remove(epf);
 	epf->driver = NULL;
 
 	return ret;