Fixes CMake lint error (#36123)
Summary:
```
Total Errors: 1
Ignoring file: aten/src/ATen/ATenConfig.cmake.in
caffe2/CMakeLists.txt:504: Extra spaces between 'if' and its () [whitespace/extra]
Ignoring file: cmake/Caffe2Config.cmake.in
Ignoring file: cmake/Caffe2ConfigVersion.cmake.in
```
Fixes that error.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/36123
Differential Revision: D20886027
Pulled By: mruberry
fbshipit-source-id: 826a8b02bb128916e3b1634f3ff312cc36e100b5
