Fix preview gamma handling

Assets/ScriptableRenderPipeline/HDRenderPipeline/SceneSettings/Resources/DrawSssProfile.shader

                 float3 M = S * (exp(-r * S) + exp(-r * S * (1.0 / 3.0))) / (8 * PI * r);
 
                 // N.b.: we multiply by the surface albedo of the actual geometry during shading.
-                // Apply gamma for visualization only.
-                return float4(pow(M * _SurfaceAlbedo.rgb, 1.0 / 3.0), 1);
+                // Apply gamma for visualization only. Do not apply gamma to the color.
+                return float4(pow(M, 1.0 / 3.0) * _SurfaceAlbedo.rgb, 1);
             }
             ENDHLSL
         }

Assets/ScriptableRenderPipeline/HDRenderPipeline/SceneSettings/Resources/DrawTransmittanceGraph.shader

             float4 Frag(Varyings input) : SV_Target
             {
                 float  d = (_ThicknessRemap.x + input.texcoord.x * (_ThicknessRemap.y - _ThicknessRemap.x));
-                float3 T = ComputeTransmittance(_ShapeParameter.rgb, _VolumeAlbedo.rgb, d, 1);
+                float3 T = ComputeTransmittance(_ShapeParameter.rgb, float3(1, 1, 1), d, 1);
-                // Apply gamma for visualization only.
-                return float4(pow(T, 1.0 / 3), 1);
+                // Apply gamma for visualization only. Do not apply gamma to the color.
+                return float4(pow(T, 1.0 / 3) * _VolumeAlbedo.rgb, 1);
             }
             ENDHLSL
         }