[c++] Generate correct type for enum lookup method. Issue aeron-io#435.

Author: mjpt777

sbe-tool/src/main/java/uk/co/real_logic/sbe/generation/cpp/CppGenerator.java

@@ -720,7 +720,7 @@ private CharSequence generateEnumValues(final List<Token> tokens, final Token en
 
  private static CharSequence generateEnumLookupMethod(final List<Token> tokens, final Token encodingToken)
  {
- final String enumName = formatClassName(encodingToken.name());
+ final String enumName = formatClassName(encodingToken.contextualTypeName());
  final StringBuilder sb = new StringBuilder();
 
  sb.append(String.format(