drm/bridge: tfp410: Fix setup and hold time calculation

This fixes a bug in the calculation of the setup and hold times based on
the deskew configuration.

Signed-off-by: Ricardo Cañuelo <ricardo.canuelo@collabora.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200617094633.19663-5-ricardo.canuelo@collabora.com