drm/i915/mst: Reject modes that require the bigjoiner

We have no bigjoiner support in the MST code, so .mode_valid()
pretending otherwise is just going to result black screens for
users. Reject any mode that needs the joiner.

Cc: stable@vger.kernel.org
Cc: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Fixes: d51f25eb ("drm/i915: Add DSC support to MST path")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231127145028.4899-3-ville.syrjala@linux.intel.comReviewed-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/display/intel_dp_mst.c

@@ -1332,6 +1332,10 @@ intel_dp_mst_mode_valid_ctx(struct drm_connector *connector,
 	if (intel_dp_need_bigjoiner(intel_dp, mode->hdisplay, target_clock)) {
 		bigjoiner = true;
 		max_dotclk *= 2;
+
+		/* TODO: add support for bigjoiner */
+		*status = MODE_CLOCK_HIGH;
+		return 0;
 	}
 
 	if (DISPLAY_VER(dev_priv) >= 10 &&