[llvm-cgdata] Fix -Wcovered-switch-default (NFC)

/llvm-project/llvm/tools/llvm-cgdata/llvm-cgdata.cpp:349:3:
error: default label in switch which covers all enumeration values [-Werror,-Wcovered-switch-default]
  default:
  ^
1 error generated.

llvm/tools/llvm-cgdata/llvm-cgdata.cpp

@@ -346,9 +346,7 @@ int llvm_cgdata_main(int argc, char **argvNonConst, const llvm::ToolContext &) {
     return merge_main(argc, argv);
   case CGDataAction::Show:
     return show_main(argc, argv);
-  default:
-    llvm_unreachable("unrecognized action");
   }
 
-  return 1;
+  llvm_unreachable("unrecognized action");
 }