usb-host: fix splitted transfers

USBPacket->actual_length wasn't updated correctly for USBPackets
splitted into multiple urbs.  Fix it.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
diff --git a/hw/usb/host-linux.c b/hw/usb/host-linux.c
index e3d394f..aa77b77 100644
--- a/hw/usb/host-linux.c
+++ b/hw/usb/host-linux.c
@@ -366,8 +366,11 @@
         if (p) {
             switch (aurb->urb.status) {
             case 0:
-                p->actual_length = aurb->urb.actual_length;
-                p->status = USB_RET_SUCCESS; /* Clear previous ASYNC status */
+                p->actual_length += aurb->urb.actual_length;
+                if (!aurb->more) {
+                    /* Clear previous ASYNC status */
+                    p->status = USB_RET_SUCCESS;
+                }
                 break;
 
             case -EPIPE: