kvm: add stub for kvm_irqchip_update_msi_route

ppc64 build needs this stub to build with virtio enabled.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

kvm-all.c

@@ -1181,6 +1181,11 @@ static int kvm_irqchip_assign_irqfd(KVMState *s, int fd, int virq, bool assign)
 {
     abort();
 }
+
+int kvm_irqchip_update_msi_route(KVMState *s, int virq, MSIMessage msg)
+{
+    return -ENOSYS;
+}
 #endif /* !KVM_CAP_IRQ_ROUTING */
 
 int kvm_irqchip_add_irqfd_notifier(KVMState *s, EventNotifier *n, int virq)