Fix some uses of dyn_cast to be uses of cast.

llvm-svn: 40443
diff --git a/llvm/lib/CodeGen/DwarfWriter.cpp b/llvm/lib/CodeGen/DwarfWriter.cpp
index 257a776..e157e58 100644
--- a/llvm/lib/CodeGen/DwarfWriter.cpp
+++ b/llvm/lib/CodeGen/DwarfWriter.cpp
@@ -1546,7 +1546,7 @@
                 break;
               }
               
-              FromTy = dyn_cast<DerivedTypeDesc>(FromTy)->getFromType();
+              FromTy = cast<DerivedTypeDesc>(FromTy)->getFromType();
             }
             
             // Unless we have a bit field.