kvm-stub: fix compilation

Non-KVM targets fail compilation on the uq/master branch.
Fix the prototype of kvm_irqchip_add_irqfd_notifier to match
the one in kvm-all.c.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
diff --git a/kvm-stub.c b/kvm-stub.c
index 7b2233a..806b044 100644
--- a/kvm-stub.c
+++ b/kvm-stub.c
@@ -135,7 +135,8 @@
     return -ENOSYS;
 }
 
-int kvm_irqchip_add_irqfd_notifier(KVMState *s, EventNotifier *n, int virq)
+int kvm_irqchip_add_irqfd_notifier(KVMState *s, EventNotifier *n,
+                                   EventNotifier *rn, int virq)
 {
     return -ENOSYS;
 }