net/mlx5: check for allocation failure in mlx5_ft_pool_init()

Add a check for if the kzalloc() fails.

Fixes: 4a98544d ("net/mlx5: Move chains ft pool to be used by all firmware steering")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>