staging: dwc2: optimize dwc2_hc_handle_tt_clear() a bit

Make dwc2_hc_handle_tt_clear() return early if the device is
hi-speed.

Signed-off-by: Paul Zimmerman <paulz@synopsys.com>
Tested-by: Stephen Warren <swarren@wwwdotorg.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>