vfio: fix race condition with sysfs

vfio: fix race condition with sysfs

This fix treats a 0 return value from vfio_open_group_fd
in vfio_get_group_fd as the intended error condition instead
of putting an incorrect 0 file descriptor in the vfio_group table.

Sometimes, the creation of device files in sysfs is not
instantaneously causing vfio_open_groupfd to return 0.
This has been observed when hot removing/adding multiple
NVMe devices (>=4).

Fixes: 340b7bb8d583 ("vfio: extend data structure for multi container")
Cc: stable@dpdk.org
Signed-off-by: Michael Haeuptle <michael.haeuptle@hpe.com>
Acked-by: Darek Stojaczyk <dariusz.stojaczyk@intel.com>
Acked-by: Anatoly Burakov <anatoly.burakov@intel.com>