Fix gen benchmark script.

The script was using the wrong variable when writing the files and
always attempting to use a temp folder, even when not doing the stale
cache check. Fix variables to correct usage.

Change-Id: I8140f4565354ab71cbe960ba7b95babc74b0f7e0
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/257914
Commit-Queue: James Price <jrprice@google.com>
Reviewed-by: James Price <jrprice@google.com>
Auto-Submit: dan sinclair <dsinclair@chromium.org>
Commit-Queue: dan sinclair <dsinclair@chromium.org>

src/tint/cmd/bench/generate_benchmark_inputs.py

diff --git a/src/tint/cmd/bench/generate_benchmark_inputs.py b/src/tint/cmd/bench/generate_benchmark_inputs.py
index b750d99..6e722e6 100644
--- a/src/tint/cmd/bench/generate_benchmark_inputs.py
+++ b/src/tint/cmd/bench/generate_benchmark_inputs.py
@@ -104,9 +104,9 @@
             subprocess.run(tint_args, check=True)
 
             # Rewrite the file without CRLF line endings.
-            with open(tmp_wgsl_path, 'r') as file:
+            with open(wgsl_path, 'r') as file:
                 wgsl = file.read()
-            with open(tmp_wgsl_path, 'w', newline='\n') as file:
+            with open(wgsl_path, 'w', newline='\n') as file:
                 file.write(wgsl)
 
             # Check if the generated content is different to the current file.