When the fail-safe device is reconfigured, it attempts to register
again for the sub-devices LSC and RMV events.
Prevent an event registration if it is already done.
Fixes: 598fb8aec6 ("net/failsafe: support device removal")
Cc: stable@dpdk.org
Signed-off-by: Matan Azrad <matan@mellanox.com>
Acked-by: Gaetan Rivet <gaetan.rivet@6wind.com>