PCI: Add pci_device_to_OF_node() stub for !CONFIG_OF

Add a stub for pci_device_to_OF_node() so drivers don't need to
use #ifdef CONFIG_OF around calls to it.

Signed-off-by: Kevin Hao <haokexin@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

include/linux/pci.h

@@ -1847,6 +1847,8 @@ static inline void pci_set_of_node(struct pci_dev *dev) { }
 static inline void pci_release_of_node(struct pci_dev *dev) { }
 static inline void pci_set_bus_of_node(struct pci_bus *bus) { }
 static inline void pci_release_bus_of_node(struct pci_bus *bus) { }
+static inline struct device_node *
+pci_device_to_OF_node(const struct pci_dev *pdev) { return NULL; }
 #endif  /* CONFIG_OF */
 
 #ifdef CONFIG_EEH