Fix doxygen for src/transform/first_index_offset.h

Change-Id: I29cee48b3b757373f90768af545a7449f60a5f26
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/35142
Commit-Queue: David Neto <dneto@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Auto-Submit: David Neto <dneto@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>

src/transform/first_index_offset.h

diff --git a/src/transform/first_index_offset.h b/src/transform/first_index_offset.h
index d3fc209..ae28629 100644
--- a/src/transform/first_index_offset.h
+++ b/src/transform/first_index_offset.h
@@ -95,7 +95,6 @@
   /// @param field_name name of field in firstVertex/Instance buffer
   /// @param buffer_var variable of firstVertex/Instance buffer
   /// @param func function to modify
-  /// @returns true if it was able to add constant to function
   void AddFirstIndexOffset(const std::string& original_name,
                            const std::string& field_name,
                            ast::Variable* buffer_var,