Merge pull request #1128 from Unity-Technologies/lw/fix_pbr_shader

Fixed a compilation error in LW PBR Standard shader

ScriptableRenderPipeline/LightweightPipeline/LWRP/ShaderLibrary/InputSurfacePBR.hlsl

 #define LIGHTWEIGHT_INPUT_SURFACE_PBR_INCLUDED
 
 #include "Core.hlsl"
+#include "CoreRP/ShaderLibrary/CommonMaterial.hlsl"
 
 CBUFFER_START(UnityPerMaterial)
 float4 _MainTex_ST;