net/mlx5: DR, Remove useless set memory to zero use memset()

The memory return by kzalloc() has already be set to zero, so
remove useless memset(0).

Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>