net/mlx5e: Fix compilation error in TLS code

In the cited patch below, the Kconfig flags combination of:
CONFIG_MLX5_FPGA is not set
CONFIG_MLX5_TLS=y
CONFIG_MLX5_EN_TLS=y

leads to the compilation error:

./include/linux/mlx5/device.h:61:39: error: invalid application of
sizeof to incomplete type struct mlx5_ifc_tls_flow_bits.

Fix it.

Fixes: 90687e1a9a50 ("net/mlx5: Kconfig, Better organize compilation flags")
Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
CC: Mao Wenan <maowenan@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>