drm/i915: warn about missing ->get_buf_trans initialization

Make sure each DDI platform has sane ->get_buf_trans initialized.
Suggested-by: NMatt Roper <matthew.d.roper@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Reviewed-by: NArun R Murthy <arun.r.murthy@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220503082134.4128355-1-jani.nikula@intel.com

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

@@ -1673,7 +1673,9 @@ void intel_ddi_buf_trans_init(struct intel_encoder *encoder)
 		encoder->get_buf_trans = skl_get_buf_trans;
 	} else if (IS_BROADWELL(i915)) {
 		encoder->get_buf_trans = bdw_get_buf_trans;
-	} else {
+	} else if (IS_HASWELL(i915)) {
 		encoder->get_buf_trans = hsw_get_buf_trans;
+	} else {
+		MISSING_CASE(INTEL_INFO(i915)->platform);
 	}
 }