[PATCH] ehci: add tt_usecs

This adds the field tt_usecs to ehci_qh and ehci_iso_stream, and sets it
appropriately when setting them up as periodic endpoints.  It records
the transation translator's think_time (added in last patch) plus the
downstream (i.e. low or full speed) bustime of the transfer associated
with each interrupt or iso frame, as calculated by usb_calc_bus_time.

Signed-off-by: Dan Streetman <ddstreet@ieee.org>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>