microblaze/PCI: fix "io_offset undeclared" error

There is a compile error for microblaze pci because io_offset is not
declared. This patch adds declaration of io_offset.

[bhelgaas: I introduced this problem with 58de74b8]
Signed-off-by: Hiroo MATSUMOTO <matsumoto.hiroo@jp.fujitsu.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

arch/microblaze/pci/pci-common.c

@@ -1422,6 +1422,7 @@ int pcibios_enable_device(struct pci_dev *dev, int mask)
 
 static void __devinit pcibios_setup_phb_resources(struct pci_controller *hose, struct list_head *resources)
 {
+	unsigned long io_offset;
 	struct resource *res;
 	int i;