Constify getter methods.

llvm-svn: 68745
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfWriter.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfWriter.cpp
index 21bfbe4..508d402 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfWriter.cpp
+++ b/llvm/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; }