usb: async control xfer fixup

Need to clear p->result after copying setup data using usb_packet_copy()
because we'll reuse the USBPacket for the data transfer.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

hw/usb/core.c

@@ -107,6 +107,7 @@ static int do_token_setup(USBDevice *s, USBPacket *p)
     }
 
     usb_packet_copy(p, s->setup_buf, p->iov.size);
+    p->result = 0;
     s->setup_len   = (s->setup_buf[7] << 8) | s->setup_buf[6];
     s->setup_index = 0;
 

hw/usb/host-linux.c

@@ -1045,6 +1045,7 @@ static int usb_host_handle_control(USBDevice *dev, USBPacket *p,
 
     /* Note request is (bRequestType << 8) | bRequest */
     trace_usb_host_req_control(s->bus_num, s->addr, p, request, value, index);
+    assert(p->result == 0);
 
     switch (request) {
     case DeviceOutRequest | USB_REQ_SET_ADDRESS: