This is a nasty bug. Since kobject count will be reduced by zero by
edac_mc_del_mc(), and this triggers the kobj release method, the
mci memory will be freed automatically. So, all we have left is ctl_name,
as shown by enabling debug:

[   80.822186] EDAC DEBUG: in drivers/edac/edac_mc_sysfs.c, line at 1020: edac_remove_sysfs_mci_device()  remove_link
[   80.832590] EDAC DEBUG: in drivers/edac/edac_mc_sysfs.c, line at 1024: edac_remove_sysfs_mci_device()  remove_mci_instance
[   80.843776] EDAC DEBUG: in drivers/edac/edac_mc_sysfs.c, line at 640: edac_mci_control_release() mci instance idx=0 releasing
[   80.855163] EDAC MC: Removed device 0 for i7core_edac.c i7 core #0: DEV 0000:3f:03.0
[   80.862936] EDAC DEBUG: in drivers/edac/i7core_edac.c, line at 2089: (null): free structs
[   80.871134] EDAC DEBUG: in drivers/edac/edac_mc.c, line at 238: edac_mc_free()
[   80.878379] EDAC DEBUG: in drivers/edac/edac_mc_sysfs.c, line at 726: edac_mc_unregister_sysfs_main_kobj()
[   80.888043] EDAC DEBUG: in drivers/edac/i7core_edac.c, line at 1232: drivers/edac/i7core_edac.c: i7core_put_devices()

Also, kfree(mci) shouldn't happen at the kobj.release, as it happens
when edac_remove_sysfs_mci_device() is called, but the logic is:
	edac_remove_sysfs_mci_device(mci);
	edac_printk(KERN_INFO, EDAC_MC,
		"Removed device %d for %s %s: DEV %s\n", mci->mc_idx,
		mci->mod_name, mci->ctl_name, edac_dev_name(mci));
So, as the edac_printk() needs the mci struct, this generates an OOPS.
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>