sparc64: Fix build errors with gcc-4.6.0

Most of the warnings emitted (we fail arch/sparc file
builds with -Werror) were legitimate but harmless, however
one case (n2_pcr_write) was a genuine bug.

Based almost entirely upon a patch by Sam Ravnborg.

Reported-by: Dennis Gilmore <dennis@ausil.us>
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/sparc/kernel/pci.c

@@ -675,6 +675,7 @@ static void __devinit pci_bus_register_of_sysfs(struct pci_bus *bus)
 		 * humanoid.
 		 */
 		err = sysfs_create_file(&dev->dev.kobj, &dev_attr_obppath.attr);
+		(void) err;
 	}
 	list_for_each_entry(child_bus, &bus->children, node)
 		pci_bus_register_of_sysfs(child_bus);