Fixed filename in the comments.

Author: palimondo

benchmark/single-source/Prefix.swift.gyb

@@ -1,4 +1,4 @@
-//===--- Suffix.swift ---------------------------------------------------===//
+//===--- Prefix.swift -----------------------------------------------------===//
 //
 // This source file is part of the Swift.org open source project
 //
@@ -13,7 +13,7 @@
 % # Ignore the following warning. This _is_ the correct file to edit.
 ////////////////////////////////////////////////////////////////////////////////
 // WARNING: This file is manually generated from .gyb template and should not
-// be directly modified. Instead, make changes to Suffix.swift.gyb and run
+// be directly modified. Instead, make changes to Prefix.swift.gyb and run
 // scripts/generate_harness/generate_harness.py to regenerate this file.
 ////////////////////////////////////////////////////////////////////////////////