Fix FastSign()

ScriptableRenderPipeline/Core/ShaderLibrary/Common.hlsl

 
 // Ref: https://twitter.com/SebAaltonen/status/878250919879639040
 // 2 mads (mad_sat and mad), faster than regular sign
-float3 FastSign(float x)
+float FastSign(float x)
-    return  saturate(x * FLT_MAX) * 2.0 - 1.0;
+    return saturate(x * FLT_MAX) * 2.0 - 1.0;
 }
 
 // Orthonormalizes the tangent frame using the Gram-Schmidt process.