[SPARK-35308][TESTS] Fix bug in SPARK-35266 that creates benchmark files in invalid path with wrong name

[byungsoo-oh]

What changes were proposed in this pull request?

This PR fixes a bug in SPARK-35266 that creates benchmark files in the invalid path with the wrong name.
e.g. For BLASBenchmark,

• AS-IS: Creates benchmarksBLASBenchmark-results.txt in {SPARK_HOME}/mllib-local/
• TO-BE: Creates BLASBenchmark-results.txt in {SPARK_HOME}/mllib-local/benchmarks/

Why are the changes needed?

As you can see in the above example, new benchmark files cannot be created as intended due to this bug.

Does this PR introduce any user-facing change?

No

How was this patch tested?

After building Spark, manually tested with the following command:

SPARK_GENERATE_BENCHMARK_FILES=1 bin/spark-submit --class \
    org.apache.spark.benchmark.Benchmarks --jars \
    "`find . -name '*-SNAPSHOT-tests.jar' -o -name '*avro*-SNAPSHOT.jar' | paste -sd ',' -`" \
    "`find . -name 'spark-core*-SNAPSHOT-tests.jar'`" \
    "org.apache.spark.ml.linalg.BLASBenchmark"

It successfully generated the benchmark files as intended (BLASBenchmark-results.txt in {SPARK_HOME}/mllib-local/benchmarks/).

[AmplabJenkins]

Can one of the admins verify this patch?

[HyukjinKwon]

I manually tested. Merged to master.