Prefer copy init over direct init. NFC.

llvm-svn: 239327
diff --git a/llvm/lib/IR/AsmWriter.cpp b/llvm/lib/IR/AsmWriter.cpp
index b147f9d..0744fdf 100644
--- a/llvm/lib/IR/AsmWriter.cpp
+++ b/llvm/lib/IR/AsmWriter.cpp
@@ -2143,7 +2143,7 @@
     Out << '\n';
 
     // Split the string into lines, to make it easier to read the .ll file.
-    StringRef Asm(M->getModuleInlineAsm());
+    StringRef Asm = M->getModuleInlineAsm();
     do {
       StringRef Front;
       std::tie(Front, Asm) = Asm.split('\n');