Constify getter methods.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@68745 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/AsmPrinter/DwarfWriter.cpp b/lib/CodeGen/AsmPrinter/DwarfWriter.cpp
index 21bfbe4..508d402 100644
--- a/lib/CodeGen/AsmPrinter/DwarfWriter.cpp
+++ b/lib/CodeGen/AsmPrinter/DwarfWriter.cpp
@@ -858,7 +858,7 @@
   //===--------------------------------------------------------------------===//
   // Accessors.
   //
-  AsmPrinter *getAsm() const { return Asm; }
+  const AsmPrinter *getAsm() const { return Asm; }
   MachineModuleInfo *getMMI() const { return MMI; }
   const TargetAsmInfo *getTargetAsmInfo() const { return TAI; }
   const TargetData *getTargetData() const { return TD; }