sfc: fix attempt to translate invalid filter ID

When filter insertion fails with no rollback, we were trying to convert
 EFX_EF10_FILTER_ID_INVALID to an id to store in 'ids' (which is either
 vlan->uc or vlan->mc).  This would WARN_ON_ONCE and then record a bogus
 filter ID of 0x1fff, neither of which is a good thing.

Fixes: 0ccb998b

 ("sfc: fix filter_id misinterpretation in edge case")
Signed-off-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>