vdpa/mlx5: fix event channel setup

vdpa/mlx5: fix event channel setup

During vDPA device setup, if some error happens, event channel
release stucks at polling event channel.

Event channel fd is set to non-blocking in cqe setup, so if any
error happens before this function and after event channel created,
the pooling before releasing resources will stuck.

This patch moves event channel to non-blocking mode right after
creation.

Fixes: 8395927cdfaf ("vdpa/mlx5: prepare HW queues")
Cc: stable@dpdk.org
Signed-off-by: Xueming Li <xuemingl@nvidia.com>
Acked-by: Matan Azrad <matan@nvidia.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>