net/mlx5: Fix memory leak in IPsec RoCE creation

During IPsec RoCE TX creation a struct for the flow group creation is
allocated, but never freed. Free that struct once it is no longer in use.

Fixes: 22551e77

 ("net/mlx5: Configure IPsec steering for egress RoCEv2 traffic")
Signed-off-by: Patrisious Haddad <phaddad@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Link: https://lore.kernel.org/r/a69739482cca7176d3a466f87bbf5af1250b09bb.1677056384.git.leon@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>