drm: bridge: nwl-dsi: Drop unused nwl_dsi_plat_clk_config

nwl_dsi_plat_clk_config structure added in below commit but not
used anywhere in the driver.

commit <44cfc623> ("drm/bridge: Add NWL MIPI DSI host controller
support")

Drop it.

Cc: Guido Günther <agx@sigxcpu.org>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Guido Günther <agx@sigxcpu.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210704093433.27717-1-jagan@amarulasolutions.com