usb: update config descriptors to identify number of interfaces

Previously we relied on the .bNumInterfaces, but that won't always be
accurate after the introduction of grouped interfaces.

Signed-off-by: Brad Hards <bradh@frogmouth.net>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

hw/usb-hub.c

@@ -119,6 +119,7 @@ static const USBDescDevice desc_device_hub = {
             .bNumInterfaces        = 1,
             .bConfigurationValue   = 1,
             .bmAttributes          = 0xe0,
+            .nif = 1,
             .ifs = &desc_iface_hub,
         },
     },