net/mlx5: Remove return statement exist at the end of void function

void function return statements are not generally useful.

Signed-off-by: Wenpeng Liang <liangwenpeng@huawei.com>
Signed-off-by: Weihang Li <liweihang@huawei.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>