microblaze: pci: export isa_io_base to fix link errors

ERROR: "isa_io_base" [sound/pci/vx222/snd-vx222.ko] undefined!
ERROR: "isa_io_base" [sound/pci/trident/snd-trident.ko] undefined!
ERROR: "isa_io_base" [sound/pci/snd-via82xx.ko] undefined!
...
ERROR: "isa_io_base" [drivers/watchdog/wdt_pci.ko] undefined!
ERROR: "isa_io_base" [drivers/watchdog/pcwd_pci.ko] undefined!
ERROR: "isa_io_base" [drivers/video/vgastate.ko] undefined!
...
ERROR: "isa_io_base" [drivers/video/fbdev/cirrusfb.ko] undefined!
ERROR: "isa_io_base" [drivers/video/fbdev/arkfb.ko] undefined!
ERROR: "isa_io_base" [drivers/usb/host/uhci-hcd.ko] undefined!
ERROR: "isa_io_base" [drivers/usb/host/isp1362-hcd.ko] undefined!
ERROR: "isa_io_base" [drivers/tty/serial/jsm/jsm.ko] undefined!
ERROR: "isa_io_base" [drivers/tty/serial/8250/8250_pci.ko] undefined!
...
ERROR: "isa_io_base" [drivers/scsi/qla2xxx/qla2xxx.ko] undefined!
ERROR: "isa_io_base" [drivers/scsi/ppa.ko] undefined!
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>

arch/microblaze/pci/pci-common.c

@@ -48,6 +48,8 @@ static int global_phb_number;		/* Global phb counter */
 resource_size_t isa_mem_base;
 
 unsigned long isa_io_base;
+EXPORT_SYMBOL(isa_io_base);
+
 static int pci_bus_count;
 
 struct pci_controller *pcibios_alloc_controller(struct device_node *dev)