Fix hipification issue (#121107)
Differential Revision: D54470055
```
buck-out/v2/gen/fbcode/713b128926d8b21f/caffe2/__ATen-hip__/buck-headers/ATen/native/hip/MemoryAccess.cuh:201:61: error: comparison of integers of different signs: 'R' (aka 'unsigned int') and 'int' [-Werror,-Wsign-compare]
return ((threadIdx.x + thread_work_elem*num_threads()) < remaining);
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~
```
```
buck-out/v2/gen/fbcode/713b128926d8b21f/caffe2/__ATen-hip__/buck-headers/ATen/native/hip/MemoryAccess.cuh:223:15: error: unused variable 'to' [-Werror,-Wunused-variable]
scalar_t *to = reinterpret_cast<scalar_t *>(data[0]) + block_work_size() * idx;
^
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/121107
Approved by: https://github.com/chenyang78
