drm/ingenic: Compute timings according to adjusted_mode->crtc_*

The adjusted_mode->crtc_* fields contain the values adjusted for the
hardware, and are the ones that should be written to the registers.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20201119155559.14112-2-paul@crapouillou.net