USB: dummy-hcd needs the has_tt flag

Like with other host controllers capable of operating at both high
speed and full speed, we need to indicate that the emulated controller
presented by dummy-hcd has this ability.  Otherwise usbcore will not
accept full-speed gadgets under dummy-hcd.  This patch (as1469) sets
the appropriate has_tt flag.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>