Fix wrong preprocessor test (for PR 1009675)

https://github.com/Unity-Technologies/ScriptableRenderPipeline/pull/1305

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/Lit/ShaderPass/LitDepthPass.hlsl

     #ifdef ATTRIBUTES_NEED_TEXCOORD3
     #define VARYINGS_NEED_TEXCOORD3
     #endif
-    #if ATTRIBUTES_NEED_COLOR
+    #ifdef ATTRIBUTES_NEED_COLOR
     #define VARYINGS_NEED_COLOR
     #endif
 #endif

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/Lit/ShaderPass/LitDistortionPass.hlsl

     #ifdef ATTRIBUTES_NEED_TEXCOORD3
     #define VARYINGS_NEED_TEXCOORD3
     #endif
-    #if ATTRIBUTES_NEED_COLOR
+    #ifdef ATTRIBUTES_NEED_COLOR
     #define VARYINGS_NEED_COLOR
     #endif
 #endif

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/Lit/ShaderPass/LitVelocityPass.hlsl

     #ifdef ATTRIBUTES_NEED_TEXCOORD3
     #define VARYINGS_NEED_TEXCOORD3
     #endif
-    #if ATTRIBUTES_NEED_COLOR
+    #ifdef ATTRIBUTES_NEED_COLOR
     #define VARYINGS_NEED_COLOR
     #endif
 #endif