nfp: use correct define to return NONE fec

struct ethtool_fecparam carries bitmasks not bit numbers.
We want to return 1 (NONE), not 0.

Fixes: 0d087093 ("nfp: implement ethtool FEC mode settings")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Reviewed-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>