Fixed tvm to v0.4 release

[lebeg]

Description

The submodule sha was pointing to HEAD instead of the v0.4 release and thus failing tests on the CI frequently.

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ERROR: test_tvm_bridge.test_tvm_bridge
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Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/nose/case.py", line 197, in runTest
    self.test(*self.arg)
  File "/work/mxnet/tests/python/gpu/test_tvm_bridge.py", line 61, in test_tvm_bridge
    check(tgt, dtype)
  File "/work/mxnet/tests/python/gpu/test_tvm_bridge.py", line 46, in check
    f = tvm.build(s, [x, y, zz, scale])
  File "/usr/local/lib/python2.7/dist-packages/tvm-0.5.dev0-py2.7-linux-x86_64.egg/tvm/build_module.py", line 501, in build
    mhost = codegen.build_module(fhost, str(target_host))
  File "/usr/local/lib/python2.7/dist-packages/tvm-0.5.dev0-py2.7-linux-x86_64.egg/tvm/codegen.py", line 20, in build_module
    return _Build(lowered_func, target)
  File "/usr/local/lib/python2.7/dist-packages/tvm-0.5.dev0-py2.7-linux-x86_64.egg/tvm/_ffi/_ctypes/function.py", line 185, in __call__
    ctypes.byref(ret_val), ctypes.byref(ret_tcode)))
  File "/usr/local/lib/python2.7/dist-packages/tvm-0.5.dev0-py2.7-linux-x86_64.egg/tvm/_ffi/base.py", line 66, in check_call
    raise TVMError(py_str(_LIB.TVMGetLastError()))
TVMError: [22:55:55] /tmp/tvm/src/codegen/codegen.cc:27: Check failed: bf != nullptr Target llvm is not enabled

[lebeg]

Just discovered that it has been fixed with #12479 already.