usb: fix interface initialization

zero is a valid interface number, so don't use it when resetting the
endpoints.
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

hw/usb.h

@@ -145,6 +145,8 @@
 #define USB_ENDPOINT_XFER_INT		3
 #define USB_ENDPOINT_XFER_INVALID     255
 
+#define USB_INTERFACE_INVALID         255
+
 typedef struct USBBus USBBus;
 typedef struct USBBusOps USBBusOps;
 typedef struct USBPort USBPort;

hw/usb/core.c

@@ -566,8 +566,8 @@ void usb_ep_reset(USBDevice *dev)
         dev->ep_out[ep].pid = USB_TOKEN_OUT;
         dev->ep_in[ep].type = USB_ENDPOINT_XFER_INVALID;
         dev->ep_out[ep].type = USB_ENDPOINT_XFER_INVALID;
-        dev->ep_in[ep].ifnum = 0;
-        dev->ep_out[ep].ifnum = 0;
+        dev->ep_in[ep].ifnum = USB_INTERFACE_INVALID;
+        dev->ep_out[ep].ifnum = USB_INTERFACE_INVALID;
         dev->ep_in[ep].dev = dev;
         dev->ep_out[ep].dev = dev;
         dev->ep_in[ep].pipeline = false;