The back porch timings were correct, only the sync offset was wrong.
Correct timing is now reported for 1080i and 576i, but the h offset is
incorrect for 480i for non-obvious reasons.

Fixes: fb10dc45 ("drm/vc4: hdmi: Correct HDMI timing registers for interlaced modes")
Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Link: https://lore.kernel.org/r/20221207-rpi-hvs-crtc-misc-v1-14-1f8e0770798b@cerno.techSigned-off-by: Maxime Ripard <maxime@cerno.tech>