x86/xen : Fix the wrong check in pciback

Fix the wrong check in pciback.
Signed-off-by: Yang Zhang <yang.z.zhang@Intel.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

drivers/xen/xen-pciback/pciback.h

@@ -124,7 +124,7 @@ static inline int xen_pcibk_add_pci_dev(struct xen_pcibk_device *pdev,
 static inline void xen_pcibk_release_pci_dev(struct xen_pcibk_device *pdev,
 					     struct pci_dev *dev)
 {
-	if (xen_pcibk_backend && xen_pcibk_backend->free)
+	if (xen_pcibk_backend && xen_pcibk_backend->release)
 		return xen_pcibk_backend->release(pdev, dev);
 }