Minor: fix assert in alloc_from_class

[liangcheng-yu]

Hi Anuj! This is Liangcheng.
Happened to notice a minor typo in https://github.com/erpc-io/eRPC/blob/master/src/util/huge_alloc.h#L206 which reads assert(buffer.class_size_ = class_max_size(size_class));.
It gives me compiler error when running cmake . -DPERF=OFF -DTRANSPORT=dpdk; make -j16

/home/liangcheng/eRPC/src/util/huge_alloc.h:206:31: error: suggest parentheses around assignment used as truth value [-Werror=parentheses]
  206 |     assert(buffer.class_size_ = class_max_size(size_class));
      |            ~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~

Adding set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-parentheses") to CMakeLists.txt can also resolve/bypass the error and give me successful make but I believe it was an unintended typo.

For context, my local setup:

• Operating system: 18.04.6 LTS (Bionic Beaver)
• NIC model: Mellanox Technologies MT27710 Family [ConnectX-4 Lx]
• DPDK version: 19.11.5
• rdma_core: compiled from source
• g++ (Ubuntu 11.1.0-1ubuntu1~18.04.1) 11.1.0

Thanks!