RDMA/mlx4: Return missed an error if device doesn't support steering

RDMA/mlx4: Return missed an error if device doesn't support steering

The error flow fixed in this patch is not possible because all kernel
users of create QP interface check that device supports steering before
set IB_QP_CREATE_NETIF_QP flag.

Fixes: c1c98501121e ("IB/mlx4: Add support for steerable IB UD QPs")
Link: https://lore.kernel.org/r/91c61f6e60eb0240f8bbc321fda7a1d2986dd03c.1634023677.git.leonro@nvidia.com
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>