net/mlx5: FPGA, Fix datatype mismatch

Fix warnings when building with -Wall:
drivers/net/ethernet/mellanox/mlx5/core/fpga/ipsec.c:313:36: warning: cast to restricted __be32
drivers/net/ethernet/mellanox/mlx5/core/fpga/ipsec.c:314:37: warning: cast to restricted __be32

Fixes: bebb23e6 ("net/mlx5: Accel, Add IPSec acceleration interface")
Reported-by: Or Gerlitz <gerlitz.or@gmail.com>
Signed-off-by: Ilan Tayari <ilant@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>