common/mlx5: fix probing failure code

common/mlx5: fix probing failure code

While probing the device with unsupported class, the process should
fail because no appropriate driver was found. After traversing all
the drivers, an error value should be returned for the case.

In the previous implementation, zero value indicating probing success
was wrongly returned.

Fixes: ad435d320473 ("common/mlx5: add bus-agnostic layer")
Cc: stable@dpdk.org
Signed-off-by: Bing Zhao <bingz@nvidia.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>