Update LightweightPassLitTerrain.hlsl

Addressed a comment from code review

com.unity.render-pipelines.lightweight/LWRP/ShaderLibrary/Terrain/LightweightPassLitTerrain.hlsl

 
     // Normalize weights before lighting and restore weights in final modifier functions so that the overal
     // lighting result can be correctly weighted.
-    splatControl /= (weight + 1e-3h);
+    splatControl /= (weight + HALF_MIN);
 
     half4 alpha = defaultAlpha * splatControl;