python.examples.matmul.test failed with ModuleNotFoundError

[yzhang93]

With the latest IREE and iree-llvm-sandbox, I'm having this error when running python -m python.examples.matmul.test

Traceback (most recent call last):
  File "/usr/lib/python3.9/runpy.py", line 197, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/usr/lib/python3.9/runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "/home/vivian/mmperf/external/iree-llvm-sandbox/python/examples/matmul/test.py", line 5, in <module>
    from mlir.sandbox.experts import *
  File "/home/vivian/mmperf/external/iree-llvm-sandbox/build/tools/sandbox/python_packages/mlir/sandbox/experts.py", line 1, in <module>
    from mlir.sandbox.transforms import Bufferize, LowerToLLVM, LowerVectors
  File "/home/vivian/mmperf/external/iree-llvm-sandbox/build/tools/sandbox/python_packages/mlir/sandbox/transforms.py", line 3, in <module>
    import iree.compiler.dialects.transform as transform
ModuleNotFoundError: No module named 'iree.compiler.dialects.transform'