drm/bridge: lontium-lt9611: drop TMDS char rate check in mode_valid

Drop manual check of the TMDS char rate in the mode_valid callback. This
check is now being performed by the core.

Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20241130-hdmi-mode-valid-v5-8-742644ec3b1f@linaro.org


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>