nfp: devlink: initialize the devlink port attribute "lanes"

The number of lanes of devlink port should be correctly initialized
when registering the port, so that the input check when running
"devlink port split <port> count <N>" can pass.

Fixes: a21cf0a8 ("devlink: Add a new devlink port lanes attribute and pass to netlink")
Signed-off-by: Yinjun Zhang <yinjun.zhang@corigine.com>
Signed-off-by: Louis Peens <louis.peens@corigine.com>
Signed-off-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>