cls_flower: Fix incorrect idr release when failing to modify rule

cls_flower: Fix incorrect idr release when failing to modify rule

When we fail to modify a rule, we incorrectly release the idr handle
of the unmodified old rule.

Fix that by checking if we need to release it.

Fixes: fe2502e49b58 ("net_sched: remove cls_flower idr on failure")
Reported-by: Vlad Buslov <[email protected]>
Reviewed-by: Roi Dayan <[email protected]>
Acked-by: Jiri Pirko <[email protected]>
Signed-off-by: Paul Blakey <[email protected]>
Signed-off-by: David S. Miller <[email protected]>