drm/panel: otm8009a: Set clock to 29.70 Mhz

The panel does not support clock frequency over 30.74 MHz. The clock
rate has been reduced to 29.70 MHz & new timings have been computed to
get a framerate of 50 fps.

Signed-off-by: Yannick Fertré <yannick.fertre@st.com>
Reviewed-by: Philippe Cornu <philippe.cornu@st.com>
Tested-by: Philippe Cornu <philippe.cornu@st.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1553155646-13636-1-git-send-email-yannick.fertre@st.com