net/mlx5: IPsec, fix memory leak at mlx5_fpga_ipsec_delete_sa_ctx

SA context is allocated at mlx5_fpga_ipsec_create_sa_ctx,
however the counterpart mlx5_fpga_ipsec_delete_sa_ctx function
nullifies sa_ctx pointer without freeing the memory allocated,
hence the memory leak.

Fix by free SA context when the SA is released.

Fixes: d6c4f029

 ("net/mlx5: Refactor accel IPSec code")
Signed-off-by: Raed Salem <raeds@mellanox.com>
Reviewed-by: Boris Pismenny <borisp@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>