Update the anti-unrolling hack

ScriptableRenderPipeline/HDRenderPipeline/Lighting/Volumetrics/Resources/VolumetricLighting.compute

     float3 totalRadiance = 0;
     float  opticalDepth  = 0;
 
-    uint sliceCountHack = max(VBUFFER_SLICE_COUNT, (uint)z0); // Prevent unrolling...
+    uint sliceCountHack = max(VBUFFER_SLICE_COUNT, (uint)depthParams.x); // Prevent unrolling...
 
 #ifdef LIGHTLOOP_TILE_PASS
     // Our voxel is not necessarily completely inside a single light cluster.