net/mlx5: fix an unused-function warning

These dummy helpers are all intended to be inline functions,
but one of them by accident came without the 'inline' keyword,
causing a harmless warning:

In file included from drivers/net/ethernet/mellanox/mlx5/core/main.c:63:
drivers/net/ethernet/mellanox/mlx5/core/accel/tls.h:79:1: error: 'mlx5_accel_tls_add_flow' defined but not used [-Werror=unused-function]
 mlx5_accel_tls_add_flow(struct mlx5_core_dev *mdev, void *flow,

Fixes: ab412e1d ("net/mlx5: Accel, add TLS rx offload routines")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>