intel_iommu: reset intr_enabled when system reset

This is found when I was debugging another problem.  Until now no bug
is reported with this but we'd better reset the IR status correctly
after a system reset.

Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/i386/intel_iommu.c

@@ -3138,6 +3138,7 @@ static void vtd_init(IntelIOMMUState *s)
     s->root = 0;
     s->root_extended = false;
     s->dmar_enabled = false;
+    s->intr_enabled = false;
     s->iq_head = 0;
     s->iq_tail = 0;
     s->iq = 0;