Use common LogBaseBuffer index generator

Shared between clustered light list gen and lookup

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/LightLoop/ClusteredUtils.hlsl

     return max(g_fClustBase, suggested_base);
 }
 
+uint GenerateLogBaseBufferIndex(uint2 tileIndex, uint numTilesX, uint numTilesY, uint eyeIndex)
+{
+    uint eyeOffset = eyeIndex * numTilesX * numTilesY;
+    return (eyeOffset + (tileIndex.y * numTilesX) + tileIndex.x);
+}
+
 #endif

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/LightLoop/LightLoopDef.hlsl

     if (g_isLogBaseBufferEnabled)
     {
         // XRTODO - DONE: Stereo-ize access to g_logBaseBuffer
-        const uint eyeOffset = unity_StereoEyeIndex * _NumTileClusteredX * _NumTileClusteredY;
-        logBase = g_logBaseBuffer[eyeOffset + (tileIndex.y * _NumTileClusteredX) + tileIndex.x];
+        const uint logBaseIndex = GenerateLogBaseBufferIndex(tileIndex, _NumTileClusteredX, _NumTileClusteredY, unity_StereoEyeIndex);
+        logBase = g_logBaseBuffer[logBaseIndex];
     }
 
     return SnapToClusterIdxFlex(linearDepth, logBase, g_isLogBaseBufferEnabled != 0);

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/LightLoop/lightlistbuild-clustered.compute

 #ifdef ENABLE_DEPTH_TEXTURE_BACKPLANE
     // XRTODO - DONE: Stereo-ize this, as this is per-eye set of tiles
     // Add eyeIndex*nrTilesY*nrTilesX to this index
-    uint logBaseIndex = (eyeIndex * nrTilesY * nrTilesX) + (tileIDX.y*nrTilesX) + tileIDX.x;
+    const uint logBaseIndex = GenerateLogBaseBufferIndex(tileIDX, nrTilesX, nrTilesY, eyeIndex);
 	if(threadID==0) g_logBaseBuffer[logBaseIndex] = suggestedBase;
 #endif
 }