xhci: reset port when disabling slot

Cc: qemu-stable@nongnu.org
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>
(cherry picked from commit 5c67dd7b)
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>

hw/usb/hcd-xhci.c

@@ -2076,6 +2076,7 @@ static TRBCCode xhci_disable_slot(XHCIState *xhci, unsigned int slotid)
 
     xhci->slots[slotid-1].enabled = 0;
     xhci->slots[slotid-1].addressed = 0;
+    xhci->slots[slotid-1].uport = NULL;
     return CC_SUCCESS;
 }