increase input shape to reduce variance (#25812)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25812
as title
Test Plan:
```
[huaminli@devvm2388.ftw3 ~/fbsource/fbcode] buck run mode/dev-nosan caffe2/benchmarks/operator_benchmark:benchmark_all_test -- --operators None --iterations 3
```
last few lines of the output P109238440
Reviewed By: mingzhe09088
Differential Revision: D17246792
fbshipit-source-id: d93ee5f404164d32210968997c6ea63b82058d2a
