ehci: Fix interrupts stopping when Interrupt Threshold Control is 8

If Interrupt Threshold Control is 8 or a multiple of 8, then
s->usbsts_frindex can become exactly 0x4000, at which point
(s->usbsts_frindex > s->frindex) will never become true, as
s->usbsts_frindex will not be lowered / reset in this case.

This patch fixes this.
Signed-off-by: NHans de Goede <hdegoede@redhat.com>
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

hw/usb/hcd-ehci.c

@@ -2413,7 +2413,7 @@ static void ehci_update_frindex(EHCIState *ehci, int frames)
         if (ehci->frindex == 0x00004000) {
             ehci_raise_irq(ehci, USBSTS_FLR);
             ehci->frindex = 0;
-            if (ehci->usbsts_frindex > 0x00004000) {
+            if (ehci->usbsts_frindex >= 0x00004000) {
                 ehci->usbsts_frindex -= 0x00004000;
             } else {
                 ehci->usbsts_frindex = 0;