CHROMIUM: drm: rockchip/dw_hdmi-rockchip: Protect against > 2GHz pixel clocks

CHROMIUM: drm: rockchip/dw_hdmi-rockchip: Protect against > 2GHz pixel clocks

Add a check just to make sure that someone doesn't try to give us a
pixel clock that is > 2GHz.  If they did that, some of our math might
overflow, so it's good to make sure we don't do it.

Change-Id: I451602f0d771bb16b399b43e376e1054b7ee060f
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Yakir Yang <ykk@rock-chips.com>
Reviewed-on: https://chromium-review.googlesource.com/284642
Reviewed-by: Alexandru Stan <amstan@chromium.org>