nfp: flower: remove unused index from nfp_fl_pedit()

Static checker warning complains on uninitialized variable:

        drivers/net/ethernet/netronome/nfp/flower/action.c:618 nfp_fl_pedit()
        error: uninitialized symbol 'idx'.

Which is actually never used from the functions that take it as
parameter. Remove it.

Fixes: 73867881 ("drivers: net: use flow action infrastructure")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Acked-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>