Don't apply _Py_OPCODE twice (#97986)
It's already applied in PyInstDecoder::opcode.
Applying it twice returns incorrect result on big endian systems.
This change fixes 14 tests in test/functorch/test_dims.py on big endian systems.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/97986
Approved by: https://github.com/Skylion007, https://github.com/kit1980
