livepatch: Improve error handling in klp_disable_func()

In case of func->state or func->old_addr not having expected values,
we'd rather bail out immediately from klp_disable_func().

This can't really happen with the current codebase, but fix this
anyway in the sake of robustness.

[jkosina@suse.com: reworded the changelog a bit]
Signed-off-by: Minfei Huang <mnfhuang@gmail.com>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>

kernel/livepatch/core.c

@@ -348,8 +348,10 @@ static void klp_disable_func(struct klp_func *func)
 {
 	struct klp_ops *ops;
 
-	WARN_ON(func->state != KLP_ENABLED);
+	if (WARN_ON(func->state != KLP_ENABLED))
-	WARN_ON(!func->old_addr);
+		return;
+	if (WARN_ON(!func->old_addr))
+		return;
 
 	ops = klp_find_ops(func->old_addr);
 	if (WARN_ON(!ops))