nfp: fill splittable of devlink_port_attrs correctly

[ Upstream commit 4abd9600 ]

The error is reflected in that it shows wrong splittable status of
port when executing "devlink port show".
The reason which leads the error is that the assigned operation of
splittable is just a simple negation operation of split and it does
not consider port lanes quantity. A splittable port should have
several lanes that can be split(lanes quantity > 1).
If without the judgement, it will show wrong message for some
firmware, such as 2x25G, 2x10G.

Fixes: a0f49b54 ("devlink: Add a new devlink port split ability attribute and pass to netlink")
Signed-off-by: Diana Wang <na.wang@corigine.com>
Reviewed-by: Louis Peens <louis.peens@corigine.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@corigine.com>
Signed-off-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>