hw/usb/hcd-ohci.c: Avoid shifting left into sign bit

Add U suffix to avoid undefined behaviour. This is only
strictly necessary for the 1<<31 cases, but we add it for the
other constants in these groups for consistency.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
