possible bug in python/fedml/core/distributed/communication/trpc/utils.py

Hi,

I was trying to launch `federate/cross_silo/cuda_rpc_fedavg_mnist_lr_example`, mapping all processes (1 server and 2 clients) to a single gpu.

it ended with error
```
File "/home/myhome/.local/lib/python3.10/site-packages/torch/distributed/rpc/backend_registry.py", line 235, in _validate_device_maps
raise ValueError(
ValueError: Node worker0 has target devices with invalid indices in its device map for worker2
device map = {device(type='cuda', index=0): device(type='cuda', index=2)}
device count = 1
```

I suspect there is a bug in `python/fedml/core/distributed/communication/trpc/utils.py`
```
# Generate Device Map for Cuda RPC
def set_device_map(options, worker_idx, device_list):
local_device = device_list[worker_idx]
for index, remote_device in enumerate(device_list):
logging.warn(f"Setting device map for client {index} as {remote_device}")
if index != worker_idx:
options.set_device_map(WORKER_NAME.format(index), {local_device: remote_device})
```
here `device_list` is a dict `{0:0, 1:0, 2:0}`, but `enumerate` iterates over its **keys** and then assigns the key (0,1,2) as `local_device`.

I tried to correct this as
```
for index, remote_device in enumerate(device_list):
logging.warn(f"Setting device map for client {index} as {device_list[remote_device]}")
if index != worker_idx:
options.set_device_map(WORKER_NAME.format(index), {local_device: device_list[remote_device]})
```
and the example worked ok.