net/mlx5e: Fix condition when retrieving PTP-rqn

When activating the PTP-RQ, redirect the RQT from drop-RQ to PTP-RQ.
Use mlx5e_channels_get_ptp_rqn to retrieve the rqn. This helper returns
a boolean (not status), hence caller should consider return value 0 as a
fail. Change the caller interpretation of the return value.

Fixes: 43ec0f41

 ("net/mlx5e: Hide all implementation details of mlx5e_rx_res")
Signed-off-by: Aya Levin <ayal@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>