[HUDI-1935] Update Logger statement of FlatteningTransformer

[veenaypatil]

What is the purpose of the pull request

This PR just updates the Logger statement as it was pointing to different class

Brief change log

Modify Logger statement of FlatteningTransformer class to

private static final Logger LOG = LogManager.getLogger(FlatteningTransformer.class);

Verify this pull request

This pull request is a trivial rework / code cleanup without any test coverage.

Committer checklist

• Has a corresponding JIRA in PR title & commit

• Commit message is descriptive of the change

• CI is green

• Necessary doc changes done or have another open PR

• For large changes, please consider breaking it into sub-tasks under an umbrella JIRA.

[codecov-commenter]

Codecov Report

Merging #2996 (9cd095d) into master (112732d) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 9cd095d differs from pull request most recent head d85df11. Consider uploading reports for the commit d85df11 to get more accurate results

@@             Coverage Diff              @@
##             master    #2996      +/-   ##
============================================
- Coverage     54.97%   54.97%   -0.01%     
+ Complexity     3845     3844       -1     
============================================
  Files           485      485              
  Lines         23436    23436              
  Branches       2494     2494              
============================================
- Hits          12884    12883       -1     
  Misses         9400     9400              
- Partials       1152     1153       +1     

Flag	Coverage Δ
hudicli	39.55% <ø> (ø)
hudiclient	∅ <ø> (∅)
hudicommon	50.31% <ø> (ø)
hudiflink	63.40% <ø> (ø)
hudihadoopmr	51.54% <ø> (ø)
hudisparkdatasource	73.33% <ø> (ø)
hudisync	46.44% <ø> (ø)
huditimelineservice	64.36% <ø> (ø)
hudiutilities	70.83% <100.00%> (-0.05%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...udi/utilities/transform/FlatteningTransformer.java	73.68% <100.00%> (ø)
...apache/hudi/utilities/deltastreamer/DeltaSync.java	70.84% <0.00%> (-0.34%)	⬇️

[wangxianghu]

LGTM

[veenaypatil]

Unit tests for hudi-spark-client failed but this change should not be the cause of it. @wangxianghu @vinothchandar can you pls merge