usb: XHCI shall not halt isochronous endpoints

According to the XHCI spec (4.10.2) the controller
never halts isochronous endpoints. This commit prevent
stop of isochronous streaming when sporadic errors
status received from backends.
Signed-off-by: NYuri Benditovich <yuri.benditovich@janustech.com>
Message-id: 20190128200444.5128-2-yuri.benditovich@janustech.com
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

hw/usb/hcd-xhci.c

@@ -1571,6 +1571,11 @@ static void xhci_stall_ep(XHCITransfer *xfer)
     uint32_t err;
     XHCIStreamContext *sctx;
 
+    if (epctx->type == ET_ISO_IN || epctx->type == ET_ISO_OUT) {
+        /* never halt isoch endpoints, 4.10.2 */
+        return;
+    }
+
     if (epctx->nr_pstreams) {
         sctx = xhci_find_stream(epctx, xfer->streamid, &err);
         if (sctx == NULL) {