platform/chrome: cros_ec_typec: Add bit offset for DP VDO

Use the right macro while constructing the DP_PORT_VDO to ensure the Pin
Assignment offsets are correct.

Fixes: 1ff5d97f ("platform/chrome: cros_ec_typec: Register port altmodes")
Signed-off-by: Prashant Malani <pmalani@chromium.org>
Acked-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Reviewed-by: Tzung-Bi Shih <tzungbi@kernel.org>
Link: https://lore.kernel.org/r/20220819190807.1275937-2-pmalani@chromium.org