clang-format.bash: Fix error message when clang-format is not found

Do not refer to a variable we just determined is empty to get the
name of the tool for the error message.  Just hard-code the name.

Utilities/Scripts/clang-format.bash

@@ -92,7 +92,7 @@ fi
 
 # Verify that we have a tool.
 if ! type -p "$clang_format" >/dev/null; then
-    echo "Unable to locate '$clang_format'"
+    echo "Unable to locate a 'clang-format' tool."
     exit 1
 fi