Update type comment

Signed-off-by: Matt Lord <mattalord@gmail.com>

go/vt/sqlparser/ast.go

@@ -1824,7 +1824,7 @@ type ColumnType struct {
  // Text field options
  Charset ColumnCharset
 
- // Enum values
+ // Enum and Set column definition values
  EnumValues []string
 }