misc/tvm: fix build on big-endian

/wrkdirs/usr/ports/misc/tvm/work/tvm-0.9.0/src/runtime/rpc/../minrpc/minrpc_server.h:785:3: error: static_assert failed due to requirement '(4321 == 1234) == 1' "MinRPC only works on little endian."

static_assert(DMLC_LITTLE_ENDIAN == 1, "MinRPC only works on little endian.");
^             ~~~~~~~~~~~~~~~~~~~~~~~