xhci: flush dequeue pointer to endpoint context

xhci: flush dequeue pointer to endpoint context

When done processing a endpoint ring we must update the dequeue pointer
in the endpoint context in guest memory.  This is needed to make sure
the guest has a correct view of things and also to make live migration
work properly, because xhci post_load restores alot of the state from
xhci data structures in guest memory.

Add xhci_set_ep_state() call to do that.

The recursive calls stopped by commit
ddb603ab6c981c1d67cb42266fc700c33e5b2d8f had the (unintentional) side
effect to hiding this bug.  xhci_set_ep_state() was called before
processing, to set the state to running, which updated the dequeue
pointer too.

Reported-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Tested-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-id: 20170331102521.29253-1-kraxel@redhat.com