drm/bridge/tc358775: Fix DSI clock division for vsync delay calculation

drm/bridge/tc358775: Fix DSI clock division for vsync delay calculation

Use the same PCLK divide option (divide DSI clock to generate pixel clock)
which is set to LVDS Configuration Register (LVCFG) also for a VSync delay
calculation. Without this change an auxiliary variable could underflow
during the calculation for some dual-link LVDS panels and then calculated
VSync delay is wrong. This leads to a shifted picture on a panel.

Tested-by: Jiri Vanek <jirivanek1@gmail.com>
Signed-off-by: Jiri Vanek <jirivanek1@gmail.com>
Reviewed-by: Vinay Simha BN <simhavcs@gmail.com>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220615222221.1501-3-jirivanek1@gmail.com