[gn build] Port 9ec5afe

Author: llvmgnsyncbot

llvm/utils/gn/secondary/llvm/lib/Frontend/HLSL/BUILD.gn

@@ -7,6 +7,6 @@ static_library("HLSL") {
   sources = [
     "CBuffer.cpp",
     "HLSLResource.cpp",
-    "HLSLRootSignature.cpp",
+    "HLSLRootSignatureUtils.cpp",
   ]
 }