drm/i915/display/tc: Only WARN once for bogus tc port flag

No need to spam syslog/console when we can ignore/fix the flag.

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201209211828.53193-1-sean@poorly.run