usb: initialise data element in Linux USB_DISCONNECT ioctl

This isn't used, but leaving it empty causes valgrind noise.

Signed-off-by: Brad Hards <bradh@frogmouth.net>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
diff --git a/usb-linux.c b/usb-linux.c
index 255009f..d958853 100644
--- a/usb-linux.c
+++ b/usb-linux.c
@@ -344,6 +344,7 @@
         for (interface = 0; interface < nb_interfaces; interface++) {
             ctrl.ioctl_code = USBDEVFS_DISCONNECT;
             ctrl.ifno = interface;
+            ctrl.data = 0;
             ret = ioctl(dev->fd, USBDEVFS_IOCTL, &ctrl);
             if (ret < 0 && errno != ENODATA) {
                 perror("USBDEVFS_DISCONNECT");