sfc: Fix lookup of default RX MAC filters when steered using ethtool

commit 385904f8 ('sfc: Don't use
efx_filter_{build,hash,increment}() for default MAC filters') used the
wrong name to find the index of default RX MAC filters at insertion/
update time.  This could result in memory corruption and would in any
case silently fail to update the filter.
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

drivers/net/ethernet/sfc/filter.c

@@ -675,7 +675,7 @@ s32 efx_filter_insert_filter(struct efx_nic *efx, struct efx_filter_spec *spec,
 		BUILD_BUG_ON(EFX_FILTER_INDEX_UC_DEF != 0);
 		BUILD_BUG_ON(EFX_FILTER_INDEX_MC_DEF !=
 			     EFX_FILTER_MC_DEF - EFX_FILTER_UC_DEF);
-		rep_index = spec->type - EFX_FILTER_INDEX_UC_DEF;
+		rep_index = spec->type - EFX_FILTER_UC_DEF;
 		ins_index = rep_index;
 
 		spin_lock_bh(&state->lock);