net/mlx5: E-Switch, Remove redundant warning when QoS enable failed

esw_vport_enable_qos can return error in cases below:
1. QoS is already enabled. Warnning is useless in this case.
2. Create scheduling element cmd failed. There is already a warning.

Remove the redundant warnning if esw_vport_enable_qos returns err.

Signed-off-by: Bodong Wang <bodong@mellanox.com>
Reviewed-by: Parav Pandit <parav@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>