mlxsw: spectrum: Use appropriate parameter name

The __mlxsw_sp_port_flood_set function is now used to configure flooding
for both FIDs and vFIDs, so change the parameter name to 'idx' instead
of 'fid'. This is also consistent with hardware documentation.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>