Fix syntax error in Core shader library

Introduced in b0a3ae7b086505371a6923da3e04204504dd2c40

com.unity.render-pipelines.core/CoreRP/ShaderLibrary/Common.hlsl

 // If any of the input parameters are NaNs, the result is a NaN.
 real SafeDiv(real numer, real denom)
 {
-    return (numer != denom) : numer / denom : 1;
+    return (numer != denom) ? numer / denom : 1;
 }
 
 // Generates a triangle in homogeneous clip space, s.t.