The FW returns zeros in case feature is not enabled, but it is better to
have the capability check and ensure that returned result is cleared.

Fixes: 3e09a427 ("RDMA/mlx5: Get ECE options from FW during create QP")
Link: https://lore.kernel.org/r/20200602125548.172654-3-leon@kernel.orgSigned-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>