[caffe2] Remove inline keyword of function CUDACachingAllocator::format_size (#100734)
Summary: `CUDACachingAllocator::format_size` is used not only in CUDACachingAllocator.cpp but also in CUDAMallocAsyncAllocator.cpp. This caused a breakage when the compiler inlined the function and the linker couldn't find it when resolving symbols for CUDAMallocAsyncAllocator.cpp.
Differential Revision: D45612790
Pull Request resolved: https://github.com/pytorch/pytorch/pull/100734
Approved by: https://github.com/interwq, https://github.com/kit1980
