vfio: fix secondary process initialization

vfio: fix secondary process initialization

When getting group fd from primary process, secondary wasn't storing
the fd anywhere, leading to a (harmless) error message in EAL logs,
and (not so harmless) potential problems when hot-unplugging devices
managed by VFIO in a secondary process.

Fix it by actually storing the group fd whenever we get a valid one
from the secondary process.

Fixes: 94c0776b1bad ("vfio: support hotplug")
Cc: stable@dpdk.org
Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>