Fixed truncation warnings in LW shaders.

ScriptableRenderPipeline/LightweightPipeline/LWRP/Shaders/LightweightShaderLibrary/Core.hlsl

 void ApplyFog(inout half3 color, half fogFactor)
 {
 #if defined(FOG_LINEAR) || defined(FOG_EXP) || defined(FOG_EXP2)
-    color = lerp(unity_FogColor, color, fogFactor);
+    color = lerp(unity_FogColor.rgb, color, fogFactor);
 #endif
 }
 #endif

ScriptableRenderPipeline/LightweightPipeline/LWRP/Shaders/LightweightStandardTerrain.shader

 
                 half3 indirectDiffuse = half3(0, 0, 0);
 #if LIGHTMAP_ON
-                float4 lightmapUV = half4(IN.uvControlAndLM.zw, 0.0, 0.0);
-                indirectDiffuse = SampleLightmap(lightmapUV, normalWS);
+                indirectDiffuse = SampleLightmap(IN.uvControlAndLM.zw, normalWS);
 #endif
 
                 half3 viewDirectionWS = SafeNormalize(_WorldSpaceCameraPos - IN.positionWS);