kobj: fix threshold_init_device/kobject_uevent_env oops

the logic in this function is just crazy.  It's recursive, but we
can circumvent the creation for the kobject and whole creation of the
threshold_block if some conditions are met.  That's why we see the
allocate_threshold_blocks so many times in the callstack, yet only a few
kobjects created.

Then we blow up in kobject_uevent_env() on the first debug printk.
Which means that we are just passing in garbage.

Man, this is one time that comments in code would have been very nice to
have, and why forward goto's into major code blocks are just evil...
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/cpu/mcheck/mce_amd_64.c

@@ -450,7 +450,8 @@ static __cpuinit int allocate_threshold_blocks(unsigned int cpu,
 	if (err)
 		goto out_free;
 
-	kobject_uevent(&b->kobj, KOBJ_ADD);
+	if (b)
+		kobject_uevent(&b->kobj, KOBJ_ADD);
 
 	return err;