net/mlx5: Fix mlx5_cmd_update_root_ft() error flow

The cited patch change mlx5_cmd_update_root_ft() to work with multiple
peer devices. However, it didn't align the error flow as well.
Hence, Fix the error code to work with multiple peer devices.

Fixes: 222dd185 ("{net/RDMA}/mlx5: introduce lag_for_each_peer")
Signed-off-by: Shay Drory <shayd@nvidia.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>