EDAC: Fix used after kfree() error in edac_unregister_sysfs()

Code flow looks like this:

  device_unregister(&mci->dev);
   -> kobject_put+0x25/0x50
    -> kobject_cleanup+0x77/0x190
      -> device_release+0x32/0xa0
	-> mci_attr_release+0x36/0x70
	  -> kfree(mci);
  bus_unregister(mci->bus);

Fix is to grab a local copy of "mci->bus" and use that when we call
bus_unregister().

Signed-off-by: Tony Luck <tony.luck@intel.com>
Acked-by: Aristeu Rozanski <aris@redhat.com>
Cc: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Cc: linux-edac <linux-edac@vger.kernel.org>
Link: http://lkml.kernel.org/r/21d595b0ab3d718d9cb206647f4ec91c05e62ec4.1461261078.git.tony.luck@intel.com
Signed-off-by: Borislav Petkov <bp@suse.de>

drivers/edac/edac_mc_sysfs.c

@@ -998,11 +998,12 @@ void edac_remove_sysfs_mci_device(struct mem_ctl_info *mci)
 
 void edac_unregister_sysfs(struct mem_ctl_info *mci)
 {
+	struct bus_type *bus = mci->bus;
 	const char *name = mci->bus->name;
 
 	edac_dbg(1, "Unregistering device %s\n", dev_name(&mci->dev));
 	device_unregister(&mci->dev);
-	bus_unregister(mci->bus);
+	bus_unregister(bus);
 	kfree(name);
 }