kobject: convert kernel_kset to be a kobject

kernel_kset does not need to be a kset, but a much simpler kobject now
that we have kobj_attributes.

We also rename kernel_kset to kernel_kobj to catch all users of this
symbol with a build error instead of an easy-to-ignore build warning.

Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/mm/slub.c b/mm/slub.c
index b6c7946..d26177f 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -4091,8 +4091,7 @@
 	struct kmem_cache *s;
 	int err;
 
-	slab_kset = kset_create_and_add("slab", &slab_uevent_ops,
-					&kernel_kset->kobj);
+	slab_kset = kset_create_and_add("slab", &slab_uevent_ops, kernel_kobj);
 	if (!slab_kset) {
 		printk(KERN_ERR "Cannot register slab subsystem.\n");
 		return -ENOSYS;