Fix a shadowed variable (#64695)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/64695
Resolves this warning:
```
caffe2/aten/src/ATen/ParallelOpenMP.h:109:63: warning: declaration of 'int64_t begin' shadows a parameter [-Wshadow=compatible-local]
109 | internal::invoke_parallel(begin, end, grain_size, [&](int64_t begin, int64_t end) {
| ~~~~~~~~^~~~~
caffe2/aten/src/ATen/ParallelOpenMP.h:86:1: note: shadowed declaration is here
85 | inline scalar_t parallel_reduce(
| ~~~~~~~~~~~~~~~~
86 | const int64_t begin,
| ^ ~
```
Test Plan: Sandcastle
Reviewed By: ngimel
Differential Revision: D30816128
fbshipit-source-id: 3adff6d94eea9fbd65885e88283cae10b87dba18
