PCI: endpoint: Fix WARN() when an endpoint driver is removed

Since there is no release callback defined for the PCI EPC device,
the below warning is thrown by driver core when a PCI endpoint driver is
removed:

  Device 'e65d0000.pcie-ep' does not have a release() function, it is broken and must be fixed. See Documentation/core-api/kobject.rst.
  WARNING: CPU: 0 PID: 139 at drivers/base/core.c:2232 device_release+0x78/0x8c

Hence, add the release callback and also move the kfree(epc) from
pci_epc_destroy() so that the epc memory is freed when all references are
dropped.

Link: https://lore.kernel.org/r/20220623003817.298173-1-yoshihiro.shimoda.uh@renesas.com
Tested-by: Vidya Sagar <vidyas@nvidia.com>
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>

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

@@ -724,7 +724,6 @@ void pci_epc_destroy(struct pci_epc *epc)
 {
 	pci_ep_cfs_remove_epc_group(epc->group);
 	device_unregister(&epc->dev);
-	kfree(epc);
 }
 EXPORT_SYMBOL_GPL(pci_epc_destroy);
 
@@ -746,6 +745,11 @@ void devm_pci_epc_destroy(struct device *dev, struct pci_epc *epc)
 }
 EXPORT_SYMBOL_GPL(devm_pci_epc_destroy);
 
+static void pci_epc_release(struct device *dev)
+{
+	kfree(to_pci_epc(dev));
+}
+
 /**
  * __pci_epc_create() - create a new endpoint controller (EPC) device
  * @dev: device that is creating the new EPC
@@ -779,6 +783,7 @@ __pci_epc_create(struct device *dev, const struct pci_epc_ops *ops,
 	device_initialize(&epc->dev);
 	epc->dev.class = pci_epc_class;
 	epc->dev.parent = dev;
+	epc->dev.release = pci_epc_release;
 	epc->ops = ops;
 
 	ret = dev_set_name(&epc->dev, "%s", dev_name(dev));