[Benchmark] fix indentation error
Because of a wrong indentation, the memory usage was calculated incorrectly
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/4941?src=pr&el=h1) Report
> Merging [#4941](https://codecov.io/gh/huggingface/transformers/pull/4941?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/699541c4b34479451c91b3c6c204d904f62bed83&el=desc) will **decrease** coverage by `0.00%`.
> The diff coverage is `0.00%`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/4941/graphs/tree.svg?width=650&height=150&src=pr&token=9qOlN6Hb1c)](https://codecov.io/gh/huggingface/transformers/pull/4941?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master    #4941      +/-   ##
==========================================
- Coverage   77.17%   77.17%   -0.01%     
==========================================
  Files         128      128              
  Lines       21723    21722       -1     
==========================================
- Hits        16764    16763       -1     
  Misses       4959     4959              
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/4941?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [src/transformers/benchmark/benchmark.py](https://codecov.io/gh/huggingface/transformers/pull/4941/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9iZW5jaG1hcmsvYmVuY2htYXJrLnB5) | `69.42% <0.00%> (+0.56%)` | :arrow_up: |
| [src/transformers/modeling\_tf\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/4941/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9tb2RlbGluZ190Zl91dGlscy5weQ==) | `87.26% <0.00%> (-0.16%)` | :arrow_down: |

------

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