Fix a merge omission that disabled diffuse light from area lights

com.unity.render-pipelines.high-definition/HDRP/Material/StackLit/StackLit.hlsl

     PreLightData_LoadLtcTransformSpecular(uv[BASE_LOBEB_IDX], BASE_LOBEB_IDX, preLightData);
 
 
-#ifdef LIT_DIFFUSE_LAMBERT_BRDF
+#ifdef USE_DIFFUSE_LAMBERT_BRDF
     preLightData.ltcTransformDiffuse = k_identity3x3;
 #else
     // TODO