Fix TVMFFIEnvSetDLPackManagedTensorAllocator to correctly return the original allocator#371

cyx-6 merged 3 commits intoapache:mainapache/tvm-ffi:mainfrom

nan2088:fix/TVMFFIEnvSetDLPackManagedTensorAllocatornan2088/tvm-ffi:fix/TVMFFIEnvSetDLPackManagedTensorAllocatorCopy head branch name to clipboard