fix(pu): fix total_loss calculation in pdqn.py

[puyuan1996]

Description

fix total_loss calculation bug in pdqn.py when using cuda.

Related Issue

TODO

Check List

• merge the latest version source branch/repo, and resolve all the conflicts
• pass style check
• pass all the tests

[codecov]

Codecov Report

Merging #504 (8683bc1) into main (96030a9) will increase coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #504      +/-   ##
==========================================
+ Coverage   85.49%   85.51%   +0.02%     
==========================================
  Files         528      528              
  Lines       43017    43091      +74     
==========================================
+ Hits        36776    36850      +74     
  Misses       6241     6241              

Flag	Coverage Δ
unittests	85.51% <ø> (+0.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
ding/policy/pdqn.py	21.48% <ø> (ø)
ding/framework/tests/test_parallel.py	92.52% <0.00%> (-3.74%)	⬇️
ding/envs/env_manager/tests/test_shm.py	88.46% <0.00%> (-3.54%)	⬇️
ding/worker/collector/marine_parallel_collector.py	89.86% <0.00%> (-1.35%)	⬇️
ding/envs/env/tests/test_ding_env_wrapper.py	72.03% <0.00%> (-0.78%)	⬇️
ding/entry/serial_entry_onpolicy_ppg.py	29.78% <0.00%> (-0.65%)	⬇️
ding/worker/learner/comm/flask_fs_learner.py	91.25% <0.00%> (-0.58%)	⬇️
ding/torch_utils/tests/test_data_helper.py	74.84% <0.00%> (-0.48%)	⬇️
ding/envs/env_manager/envpool_env_manager.py	37.34% <0.00%> (-0.46%)	⬇️
ding/entry/serial_entry_ngu.py	20.27% <0.00%> (-0.28%)	⬇️
... and 48 more

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