net/mlx5: IPsec, Fix esp modify function attribute

The function mlx5_fpga_esp_validate_xfrm_attrs is wrongly used
with negative negation as zero value indicates success but it
used as failure return value instead.

Fix by remove the unary not negation operator.

Fixes: 05564d0a

 ("net/mlx5: Add flow-steering commands for FPGA IPSec implementation")
Signed-off-by: Raed Salem <raeds@mellanox.com>
Reviewed-by: Boris Pismenny <borisp@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>