Avoid a compiler warning

Assets/ScriptableRenderPipeline/ShaderLibrary/AreaLighting.hlsl

 float PolygonIrradiance(float4x3 L)
 {
 #ifdef SPHERE_LIGHT_APPROXIMATION
+    [unroll]
     for (int i = 0; i < 4; i++)
     {
         L[i] = normalize(L[i]);
 
+    [unroll]
-        float3 V2 = L[(edge + 1) % 4];
+        float3 V2 = L[(edge + 1) & 0x3];
 
         F += INV_TWO_PI * ComputeEdgeFactor(V1, V2);
     }