video: rockchip: Add missing dpcd_write() call to link_train_ce()

video: rockchip: Add missing dpcd_write() call to link_train_ce()

Found this by comparing it to the coreboot driver, a form of this call
was introduced there in their commit b9a7877568cf ("rockchip/*: refactor
edp driver"). This is copy-pasted from U-Boot's link_train_cr() slightly
above it.

Without this on a gru-kevin chromebook, I have:

    clock recovery at voltage 0 pre-emphasis 0
    requested signal parameters: lane 0 voltage 0.4V pre_emph 3.5dB
    requested signal parameters: lane 1 voltage 0.4V pre_emph 3.5dB
    requested signal parameters: lane 2 voltage 0.4V pre_emph 3.5dB
    requested signal parameters: lane 3 voltage 0.4V pre_emph 3.5dB
    using signal parameters: voltage 0.4V pre_emph 3.5dB
    requested signal parameters: lane 0 voltage 0.4V pre_emph 3.5dB
    requested signal parameters: lane 1 voltage 0.4V pre_emph 3.5dB
    requested signal parameters: lane 2 voltage 0.4V pre_emph 3.5dB
    requested signal parameters: lane 3 voltage 0.4V pre_emph 3.5dB
    using signal parameters: voltage 0.4V pre_emph 3.5dB
    requested signal parameters: lane 0 voltage 0.4V pre_emph 3.5dB
    requested signal parameters: lane 1 voltage 0.4V pre_emph 3.5dB
    requested signal parameters: lane 2 voltage 0.4V pre_emph 3.5dB
    requested signal parameters: lane 3 voltage 0.4V pre_emph 3.5dB
    using signal parameters: voltage 0.4V pre_emph 3.5dB
    requested signal parameters: lane 0 voltage 0.4V pre_emph 3.5dB
    requested signal parameters: lane 1 voltage 0.4V pre_emph 3.5dB
    requested signal parameters: lane 2 voltage 0.4V pre_emph 3.5dB
    requested signal parameters: lane 3 voltage 0.4V pre_emph 3.5dB
    using signal parameters: voltage 0.4V pre_emph 3.5dB
    requested signal parameters: lane 0 voltage 0.4V pre_emph 3.5dB
    requested signal parameters: lane 1 voltage 0.4V pre_emph 3.5dB
    requested signal parameters: lane 2 voltage 0.4V pre_emph 3.5dB
    requested signal parameters: lane 3 voltage 0.4V pre_emph 3.5dB
    using signal parameters: voltage 0.4V pre_emph 3.5dB
    channel eq failed, ret=-5
    link train failed!
    rk_vop_probe() Device failed: ret=-5

With this, it looks like training succeeds:

    clock recovery at voltage 0 pre-emphasis 0
    requested signal parameters: lane 0 voltage 0.4V pre_emph 3.5dB
    requested signal parameters: lane 1 voltage 0.4V pre_emph 3.5dB
    requested signal parameters: lane 2 voltage 0.4V pre_emph 3.5dB
    requested signal parameters: lane 3 voltage 0.4V pre_emph 3.5dB
    using signal parameters: voltage 0.4V pre_emph 3.5dB
    requested signal parameters: lane 0 voltage 0.4V pre_emph 6dB
    requested signal parameters: lane 1 voltage 0.4V pre_emph 6dB
    requested signal parameters: lane 2 voltage 0.4V pre_emph 6dB
    requested signal parameters: lane 3 voltage 0.4V pre_emph 6dB
    using signal parameters: voltage 0.4V pre_emph 6dB
    requested signal parameters: lane 0 voltage 0.4V pre_emph 0dB
    requested signal parameters: lane 1 voltage 0.4V pre_emph 0dB
    requested signal parameters: lane 2 voltage 0.4V pre_emph 0dB
    requested signal parameters: lane 3 voltage 0.4V pre_emph 0dB
    using signal parameters: voltage 0.4V pre_emph 0dB
    channel eq at voltage 0 pre-emphasis 0
    config video failed
    rk_vop_probe() Device failed: ret=-110

The "config video failed" error also goes away when I disable higher
log levels, and it claims to have successfully probed the device.

Signed-off-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Kever Yang<kever.yang@rock-chips.com>