drm/bridge: ti-sn65dsi86: zero is never greater than an unsigned int

When we iterate over ti_sn_bridge_dp_rate_lut, there's no reason to
start at index 0 which always contains the value 0.  0 is not a valid
link rate.

This change should have no real effect but is a small cleanup.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Tested-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191218143416.v3.2.Id445d0057bedcb0a190009e0706e9254c2fd48eb@changeid