HLSL: fix return type for isfinite

The prior decomposition of isfinite was not setting the return type on the
sequence node.  (Sequence was used because there's an internal temporary
to avoid the complex rvalue problem).

Test/hlsl.isfinite.frag

@@ -1,9 +1,18 @@
 
-uniform float f;
+uniform float  f;
+uniform float2 f2;
+uniform float3 f3;
+
+bool test1(float v)
+{
+    return !isnan(v) && isfinite(v);
+}
 
 float4 main() : SV_Target0
 {
     isfinite(f);
+    isfinite(f2);
+    isfinite(f3);
 
     return 0;
 }