USB: fix regression in usbip by setting has_tt flag

This patch (as1460) fixes a regression in the usbip driver caused by
the new check for Transaction Translators in USB-2 hubs.  The root hub
registered by vhci_hcd needs to have the has_tt flag set, because it
can connect to low- and full-speed devices as well as high-speed
devices.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-and-tested-by: Nikola Ciprich <nikola.ciprich@linuxbox.cz>
CC: <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>